[ObjC ARC] Converts ios/chrome/browser/ui/tab_switcher:tab_switcher to ARC.

Automatically generated ARCMigrate commit
Notable issues:
* Replaced 2 instances of replaceOldTabModel:(TabModel**)oldTabModel withTabModel:(TabModel*)newTabModel method with an equivalent construct that does not pass pointers to pointers to objc objects. Feel free to suggest a better way that I can implement in a follow-up CL.
* some weak pointer dereferencing replaced with strong pointer dereferencing in blocks
* In tab_model_snapshot.mm, added a bridge cast. I'm not sure if this should be a conversion to std::string, because std::stringstream.operator<<(NSString*) can be both.

BUG=624363
TEST=None

Review-Url: https://codereview.chromium.org/2810193002
Cr-Commit-Position: refs/heads/master@{#468652}

ios/chrome/browser/ui/tab_switcher/BUILD.gn

@@ -50,6 +50,7 @@ bundle_data("resources") {
 }
 
 source_set("tab_switcher") {
+  configs += [ "//build/config/compiler:enable_arc" ]
   sources = [
     "tab_model_snapshot.h",
     "tab_model_snapshot.mm",

ios/chrome/browser/ui/tab_switcher/tab_model_snapshot.mm

@@ -6,6 +6,11 @@
 
 #include "base/strings/sys_string_conversions.h"
 #import "ios/chrome/browser/tabs/tab.h"
+#import "ios/chrome/browser/tabs/tab_model.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
 
 TabModelSnapshot::TabModelSnapshot(TabModel* tabModel) {
   for (Tab* tab in tabModel) {
@@ -31,7 +36,7 @@ size_t TabModelSnapshot::hashOfTheVisiblePropertiesOfATab(Tab* tab) {
   std::stringstream ss;
   // lastVisitedTimestamp is used as an approximation for whether the tab's
   // snapshot changed.
-  ss << tab.tabId << std::endl
+  ss << base::SysNSStringToUTF8(tab.tabId) << std::endl
      << base::SysNSStringToUTF8(tab.urlDisplayString) << std::endl
      << std::hexfloat << tab.lastVisitedTimestamp << std::endl;
   return std::hash<std::string>()(ss.str());

ios/chrome/browser/ui/tab_switcher/tab_switcher_button.mm

@@ -4,11 +4,14 @@
 
 #include "ios/chrome/browser/ui/tab_switcher/tab_switcher_button.h"
 
-#include "base/mac/scoped_nsobject.h"
 #import "ios/third_party/material_components_ios/src/components/Ink/src/MaterialInk.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 @interface TabSwitcherButton () {
-  base::scoped_nsobject<MDCInkTouchController> _inkTouchController;
+  MDCInkTouchController* _inkTouchController;
 }
 @end
 
@@ -17,8 +20,7 @@
 - (instancetype)initWithFrame:(CGRect)frame {
   self = [super initWithFrame:frame];
   if (self) {
-    _inkTouchController.reset(
-        [[MDCInkTouchController alloc] initWithView:self]);
+    _inkTouchController = [[MDCInkTouchController alloc] initWithView:self];
     [_inkTouchController addInkView];
     // TODO(crbug.com/606807): Adjust the desired ink color.
     [_inkTouchController defaultInkView].inkColor =

ios/chrome/browser/ui/tab_switcher/tab_switcher_cache.h

@@ -29,7 +29,7 @@ struct PendingSnapshotRequest {
 // cached and freed under memory pressure.
 @interface TabSwitcherCache : NSObject<TabModelObserver>
 
-@property(nonatomic, readonly) TabModel* mainTabModel;
+@property(weak, nonatomic, readonly) TabModel* mainTabModel;
 
 // Request a snapshot for the given |tab| of the given |size|, |completionBlock|
 // will be called with the requested snapshot. Must be called from the main

ios/chrome/browser/ui/tab_switcher/tab_switcher_cache.mm

@@ -6,9 +6,7 @@
 
 #include <unordered_map>
 
-#import "base/ios/weak_nsobject.h"
 #include "base/logging.h"
-#include "base/mac/scoped_nsobject.h"
 #include "base/strings/stringprintf.h"
 #include "base/synchronization/lock.h"
 #import "ios/chrome/browser/tabs/tab.h"
@@ -17,6 +15,10 @@
 #include "ios/chrome/common/ios_app_bundle_id_prefix.h"
 #include "ios/web/public/navigation_item.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 // The maximum amount of pixels the cache should hold.
 NSUInteger kCacheMaxPixelCount = 2048 * 1536 * 4;
@@ -34,11 +36,11 @@ const CGFloat kMaxFloatDelta = 0.01;
 @end
 
 @implementation TabSwitcherCache {
-  base::scoped_nsobject<NSCache> _cache;
+  NSCache* _cache;
   dispatch_queue_t _cacheQueue;
   // The tab models.
-  TabModel* _mainTabModel;  // weak
-  TabModel* _otrTabModel;   // weak
+  __weak TabModel* _mainTabModel;
+  __weak TabModel* _otrTabModel;
 
   // Lock protecting the pending requests map.
   base::Lock _lock;
@@ -50,7 +52,7 @@ const CGFloat kMaxFloatDelta = 0.01;
 - (instancetype)init {
   self = [super init];
   if (self) {
-    _cache.reset([[NSCache alloc] init]);
+    _cache = [[NSCache alloc] init];
     [_cache setTotalCostLimit:kCacheMaxPixelCount];
     NSNotificationCenter* nc = [NSNotificationCenter defaultCenter];
     [nc addObserver:self
@@ -71,10 +73,8 @@ const CGFloat kMaxFloatDelta = 0.01;
   [nc removeObserver:self
                 name:UIApplicationDidReceiveMemoryWarningNotification
               object:nil];
-  dispatch_release(_cacheQueue);
   [_mainTabModel removeObserver:self];
   [_otrTabModel removeObserver:self];
-  [super dealloc];
 }
 
 - (PendingSnapshotRequest)requestSnapshotForTab:(Tab*)tab
@@ -231,28 +231,39 @@ const CGFloat kMaxFloatDelta = 0.01;
   UIImage* resizedSnapshot =
       ResizeImage(image, pixelSize, ProjectionMode::kAspectFillNoClipping, YES);
   // Creates a new image with the correct |scale| attribute.
-  return [[[UIImage alloc] initWithCGImage:resizedSnapshot.CGImage
-                                     scale:screenScale
-                               orientation:UIImageOrientationUp] autorelease];
+  return [[UIImage alloc] initWithCGImage:resizedSnapshot.CGImage
+                                    scale:screenScale
+                              orientation:UIImageOrientationUp];
 }
 
 - (void)lowMemoryWarningReceived {
   [_cache removeAllObjects];
 }
 
-- (void)setMainTabModel:(TabModel*)mainTabModel
-            otrTabModel:(TabModel*)otrTabModel {
-  if (mainTabModel != _mainTabModel)
-    [self replaceOldTabModel:&_mainTabModel withTabModel:mainTabModel];
-  if (otrTabModel != _otrTabModel)
-    [self replaceOldTabModel:&_otrTabModel withTabModel:otrTabModel];
+- (void)setMainTabModel:(TabModel*)mainTabModel {
+  if (mainTabModel == _mainTabModel) {
+    return;
+  }
+
+  [_mainTabModel removeObserver:self];
+  _mainTabModel = mainTabModel;
+  [_mainTabModel addObserver:self];
 }
 
-- (void)replaceOldTabModel:(TabModel**)oldTabModel
-              withTabModel:(TabModel*)newTabModel {
-  [*oldTabModel removeObserver:self];
-  *oldTabModel = newTabModel;
-  [newTabModel addObserver:self];
+- (void)setOTRTabModel:(TabModel*)otrTabModel {
+  if (_otrTabModel == otrTabModel) {
+    return;
+  }
+
+  [_otrTabModel removeObserver:self];
+  _otrTabModel = otrTabModel;
+  [_otrTabModel addObserver:self];
+}
+
+- (void)setMainTabModel:(TabModel*)mainTabModel
+            otrTabModel:(TabModel*)otrTabModel {
+  [self setMainTabModel:mainTabModel];
+  [self setOTRTabModel:otrTabModel];
 }
 
 #pragma mark - TabModelObserver

ios/chrome/browser/ui/tab_switcher/tab_switcher_header_cell.mm

@@ -5,12 +5,15 @@
 #import "ios/chrome/browser/ui/tab_switcher/tab_switcher_header_cell.h"
 
 #include "base/logging.h"
-#include "base/mac/scoped_nsobject.h"
 #import "ios/chrome/browser/ui/tab_switcher/tab_switcher_session_cell_data.h"
 #import "ios/chrome/browser/ui/uikit_ui_util.h"
 #import "ios/third_party/material_components_ios/src/components/Palettes/src/MaterialPalettes.h"
 #import "ios/third_party/material_components_ios/src/components/Typography/src/MaterialTypography.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 // View alpha value used when the header cell is not selected.
 const CGFloat kInactiveAlpha = 0.54;
@@ -18,8 +21,8 @@ const CGFloat kImageViewWidth = 24;
 }
 
 @interface TabSwitcherHeaderCell () {
-  base::scoped_nsobject<UIImageView> _imageView;
-  base::scoped_nsobject<UILabel> _label;
+  UIImageView* _imageView;
+  UILabel* _label;
 }
 @end
 
@@ -59,11 +62,11 @@ const CGFloat kImageViewWidth = 24;
 #pragma mark - Private
 
 - (void)loadSubviews {
-  _imageView.reset([[UIImageView alloc] initWithFrame:CGRectZero]);
+  _imageView = [[UIImageView alloc] initWithFrame:CGRectZero];
   [_imageView setContentMode:UIViewContentModeCenter];
   [_imageView setTranslatesAutoresizingMaskIntoConstraints:NO];
   [_imageView setTintColor:[UIColor whiteColor]];
-  _label.reset([[UILabel alloc] initWithFrame:CGRectZero]);
+  _label = [[UILabel alloc] initWithFrame:CGRectZero];
   [_label setBackgroundColor:[UIColor clearColor]];
   [_label setTranslatesAutoresizingMaskIntoConstraints:NO];
   [_label setTextColor:[UIColor whiteColor]];
@@ -72,8 +75,8 @@ const CGFloat kImageViewWidth = 24;
   // Configure layout.
   // The icon and the title are centered within |contentView|, have a spacing of
   // one-third of icon width and the icon is on the leading side of title.
-  base::scoped_nsobject<UIStackView> stackView(
-      [[UIStackView alloc] initWithArrangedSubviews:@[ _imageView, _label ]]);
+  UIStackView* stackView =
+      [[UIStackView alloc] initWithArrangedSubviews:@[ _imageView, _label ]];
   [stackView setSpacing:kImageViewWidth / 3];
   [self.contentView addSubview:stackView];
 

ios/chrome/browser/ui/tab_switcher/tab_switcher_header_view.h

@@ -31,9 +31,9 @@
 
 @interface TabSwitcherHeaderView : UIView
 
-@property(nonatomic, assign) id<TabSwitcherHeaderViewDelegate> delegate;
-@property(nonatomic, assign) id<TabSwitcherHeaderViewDataSource> dataSource;
-@property(nonatomic, readonly) UIView* dismissButton;
+@property(nonatomic, weak) id<TabSwitcherHeaderViewDelegate> delegate;
+@property(nonatomic, weak) id<TabSwitcherHeaderViewDataSource> dataSource;
+@property(weak, nonatomic, readonly) UIView* dismissButton;
 
 // Selects the item at the specified index.
 // The delegate is not called.

ios/chrome/browser/ui/tab_switcher/tab_switcher_header_view.mm

@@ -4,9 +4,7 @@
 
 #import "ios/chrome/browser/ui/tab_switcher/tab_switcher_header_view.h"
 
-#import "base/ios/weak_nsobject.h"
 #include "base/logging.h"
-#include "base/mac/scoped_nsobject.h"
 #include "base/metrics/user_metrics_action.h"
 #import "ios/chrome/browser/ui/colors/MDCPalette+CrAdditions.h"
 #include "ios/chrome/browser/ui/rtl_geometry.h"
@@ -17,6 +15,10 @@
 #import "ios/third_party/material_components_ios/src/components/Palettes/src/MaterialPalettes.h"
 #include "ui/base/l10n/l10n_util.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 const CGFloat kCollectionViewTopMargin = 39.0;
 const CGFloat kCollectionViewHeight = 56.0;
@@ -41,7 +43,7 @@ enum PanelSelectionChangeDirection { RIGHT, LEFT };
 // we want the accessibilityFrame to resize itself using autoresizing masks.
 @interface AccessiblePanelSelectorView : UIView {
   // The delegate which receives actions.
-  base::WeakNSProtocol<id<AccessiblePanelSelectorDelegate>> _delegate;
+  __weak id<AccessiblePanelSelectorDelegate> _delegate;
 }
 - (void)setDelegate:(id<AccessiblePanelSelectorDelegate>)delegate;
 @end
@@ -49,7 +51,7 @@ enum PanelSelectionChangeDirection { RIGHT, LEFT };
 @implementation AccessiblePanelSelectorView
 
 - (void)setDelegate:(id<AccessiblePanelSelectorDelegate>)delegate {
-  _delegate.reset(delegate);
+  _delegate = delegate;
 }
 
 - (UIAccessibilityTraits)accessibilityTraits {
@@ -74,11 +76,11 @@ enum PanelSelectionChangeDirection { RIGHT, LEFT };
 @interface TabSwitcherHeaderView ()<UICollectionViewDataSource,
                                     UICollectionViewDelegate,
                                     AccessiblePanelSelectorDelegate> {
-  base::scoped_nsobject<UICollectionViewFlowLayout> _flowLayout;
-  base::scoped_nsobject<UICollectionView> _collectionView;
-  base::scoped_nsobject<AccessiblePanelSelectorView> _accessibilityView;
-  base::scoped_nsobject<UIButton> _dismissButton;
-  base::scoped_nsobject<UIView> _activeSpaceIndicatorView;
+  UICollectionViewFlowLayout* _flowLayout;
+  UICollectionView* _collectionView;
+  AccessiblePanelSelectorView* _accessibilityView;
+  UIButton* _dismissButton;
+  UIView* _activeSpaceIndicatorView;
 
   BOOL _performingUpdate;
 }
@@ -133,13 +135,14 @@ enum PanelSelectionChangeDirection { RIGHT, LEFT };
            completion:(ProceduralBlock)completion {
   DCHECK(updateBlock);
 
-  __block TabSwitcherHeaderView* weakSelf = self;
+  __weak TabSwitcherHeaderView* weakSelf = self;
   [_collectionView performBatchUpdates:^{
-    if (!weakSelf)
+    TabSwitcherHeaderView* strongSelf = weakSelf;
+    if (!strongSelf)
       return;
-    weakSelf->_performingUpdate = YES;
-    updateBlock(weakSelf);
-    weakSelf->_performingUpdate = NO;
+    strongSelf->_performingUpdate = YES;
+    updateBlock(strongSelf);
+    strongSelf->_performingUpdate = NO;
   }
       completion:^(BOOL finished) {
         // Reestablish selection after the update.
@@ -165,7 +168,7 @@ enum PanelSelectionChangeDirection { RIGHT, LEFT };
 }
 
 - (UIView*)dismissButton {
-  return _dismissButton.get();
+  return _dismissButton;
 }
 
 #pragma mark - Private
@@ -202,7 +205,7 @@ enum PanelSelectionChangeDirection { RIGHT, LEFT };
 
 - (NSArray*)indexPathArrayWithIndexes:(NSArray*)indexes {
   NSMutableArray* array =
-      [[[NSMutableArray alloc] initWithCapacity:indexes.count] autorelease];
+      [[NSMutableArray alloc] initWithCapacity:indexes.count];
   for (NSNumber* index in indexes) {
     [array
         addObject:[NSIndexPath indexPathForItem:[index intValue] inSection:0]];
@@ -211,8 +214,8 @@ enum PanelSelectionChangeDirection { RIGHT, LEFT };
 }
 
 - (void)loadSubviews {
-  base::scoped_nsobject<UICollectionViewFlowLayout> flowLayout(
-      [[UICollectionViewFlowLayout alloc] init]);
+  UICollectionViewFlowLayout* flowLayout =
+      [[UICollectionViewFlowLayout alloc] init];
   [flowLayout setMinimumLineSpacing:0];
   [flowLayout setMinimumInteritemSpacing:0];
   const CGSize cellSize =
@@ -221,9 +224,9 @@ enum PanelSelectionChangeDirection { RIGHT, LEFT };
   [flowLayout setScrollDirection:UICollectionViewScrollDirectionHorizontal];
   _flowLayout = flowLayout;
 
-  _collectionView.reset([[UICollectionView alloc]
-             initWithFrame:[self collectionViewFrame]
-      collectionViewLayout:flowLayout]);
+  _collectionView =
+      [[UICollectionView alloc] initWithFrame:[self collectionViewFrame]
+                         collectionViewLayout:flowLayout];
   [_collectionView setDelegate:self];
   [_collectionView setDataSource:self];
   [_collectionView registerClass:[TabSwitcherHeaderCell class]
@@ -237,8 +240,8 @@ enum PanelSelectionChangeDirection { RIGHT, LEFT };
   [_collectionView setAccessibilityElementsHidden:YES];
   [self addSubview:_collectionView];
 
-  _accessibilityView.reset([[AccessiblePanelSelectorView alloc]
-      initWithFrame:[self collectionViewFrame]]);
+  _accessibilityView = [[AccessiblePanelSelectorView alloc]
+      initWithFrame:[self collectionViewFrame]];
   [_accessibilityView
       setAutoresizingMask:UIViewAutoresizingFlexibleBottomMargin |
                           UIViewAutoresizingFlexibleWidth];
@@ -246,7 +249,7 @@ enum PanelSelectionChangeDirection { RIGHT, LEFT };
   [_accessibilityView setUserInteractionEnabled:NO];
   [self addSubview:_accessibilityView];
 
-  _dismissButton.reset([[UIButton alloc] initWithFrame:CGRectZero]);
+  _dismissButton = [[UIButton alloc] initWithFrame:CGRectZero];
   UIImage* dismissImage =
       [UIImage imageNamed:@"tabswitcher_tab_switcher_button"];
   dismissImage =
@@ -270,7 +273,7 @@ enum PanelSelectionChangeDirection { RIGHT, LEFT };
     @"H:[dismissButton(==buttonWidth)]-0-|",
   ];
   NSDictionary* viewsDictionary = @{
-    @"dismissButton" : _dismissButton.get(),
+    @"dismissButton" : _dismissButton,
   };
   NSDictionary* metrics = @{
     @"buttonHeight" : @(kDismissButtonHeight),
@@ -279,8 +282,7 @@ enum PanelSelectionChangeDirection { RIGHT, LEFT };
   ApplyVisualConstraintsWithMetricsAndOptions(
       constraints, viewsDictionary, metrics, LayoutOptionForRTLSupport(), self);
 
-  base::scoped_nsobject<UIView> activeSpaceIndicatorView(
-      [[UIView alloc] initWithFrame:CGRectZero]);
+  UIView* activeSpaceIndicatorView = [[UIView alloc] initWithFrame:CGRectZero];
   [activeSpaceIndicatorView
       setBackgroundColor:[[MDCPalette cr_bluePalette] tint500]];
   [activeSpaceIndicatorView

ios/chrome/browser/ui/tab_switcher/tab_switcher_model.mm

@@ -23,6 +23,10 @@
 #import "ios/chrome/browser/ui/tab_switcher/tab_switcher_model_private.h"
 #import "ios/chrome/browser/ui/tab_switcher/tab_switcher_panel_cell.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 bool TabSwitcherSessionTypeIsLocalSession(TabSwitcherSessionType sessionType) {
   return sessionType == TabSwitcherSessionType::OFF_THE_RECORD_SESSION ||
          sessionType == TabSwitcherSessionType::REGULAR_SESSION;
@@ -54,10 +58,10 @@ void FillSetUsingSessions(synced_sessions::SyncedSessions const& sessions,
   // The browser state.
   ios::ChromeBrowserState* _browserState;  // weak
   // The tab models.
-  TabModel* _mainTabModel;  // weak
-  TabModel* _otrTabModel;   // weak
+  __weak TabModel* _mainTabModel;
+  __weak TabModel* _otrTabModel;
   // The delegate for event callbacks.
-  id<TabSwitcherModelDelegate> _delegate;  // weak, owns us.
+  __weak id<TabSwitcherModelDelegate> _delegate;
   // The synced sessions. Must never be null.
   std::unique_ptr<synced_sessions::SyncedSessions> _syncedSessions;
   // The synced sessions change observer.
@@ -67,7 +71,7 @@ void FillSetUsingSessions(synced_sessions::SyncedSessions const& sessions,
   std::unique_ptr<TabModelSnapshot> _mainTabModelSnapshot;
   std::unique_ptr<TabModelSnapshot> _otrTabModelSnapshot;
   // The cache holding resized tabs snapshots.
-  base::scoped_nsobject<TabSwitcherCache> _cache;
+  TabSwitcherCache* _cache;
 }
 
 // Returns the type of the local session corresponding to the given |tabModel|.
@@ -101,23 +105,36 @@ void FillSetUsingSessions(synced_sessions::SyncedSessions const& sessions,
     _otrTabModelSnapshot.reset(new TabModelSnapshot(otrTabModel));
     [_mainTabModel addObserver:self];
     [_otrTabModel addObserver:self];
-    _cache.reset([cache retain]);
+    _cache = cache;
   }
   return self;
 }
 
 - (void)setMainTabModel:(TabModel*)mainTabModel
             otrTabModel:(TabModel*)otrTabModel {
-  [self replaceOldTabModel:&_mainTabModel withTabModel:mainTabModel];
-  [self replaceOldTabModel:&_otrTabModel withTabModel:otrTabModel];
+  [self replaceMainTabModelWithTabModel:mainTabModel];
+  [self replaceOTRTabModelWithTabModel:otrTabModel];
 }
 
-- (void)replaceOldTabModel:(TabModel**)oldTabModel
-              withTabModel:(TabModel*)newTabModel {
-  if (*oldTabModel == newTabModel)
+- (void)replaceMainTabModelWithTabModel:(TabModel*)newTabModel {
+  if (_mainTabModel == newTabModel)
     return;
-  [*oldTabModel removeObserver:self];
-  *oldTabModel = newTabModel;
+  [_mainTabModel removeObserver:self];
+  _mainTabModel = newTabModel;
+  [newTabModel addObserver:self];
+  // Calling |tabModelChanged:| may trigger an animated refresh of the
+  // Tab Switcher's collection view.
+  // Here in |replaceOldTabModel:withTabModel:| the animation is undesirable.
+  [UIView performWithoutAnimation:^{
+    [self tabModelChanged:newTabModel];
+  }];
+}
+
+- (void)replaceOTRTabModelWithTabModel:(TabModel*)newTabModel {
+  if (_otrTabModel == newTabModel)
+    return;
+  [_otrTabModel removeObserver:self];
+  _otrTabModel = newTabModel;
   [newTabModel addObserver:self];
   // Calling |tabModelChanged:| may trigger an animated refresh of the
   // Tab Switcher's collection view.
@@ -130,7 +147,6 @@ void FillSetUsingSessions(synced_sessions::SyncedSessions const& sessions,
 - (void)dealloc {
   [_mainTabModel removeObserver:self];
   [_otrTabModel removeObserver:self];
-  [super dealloc];
 }
 
 - (NSInteger)sessionCount {

ios/chrome/browser/ui/tab_switcher/tab_switcher_panel_cell.h

@@ -32,7 +32,7 @@ CGFloat tabSwitcherLocalSessionCellTopBarHeight();
 + (NSString*)identifier;
 
 // The cell delegate.
-@property(nonatomic, assign) id<SessionCellDelegate> delegate;
+@property(nonatomic, unsafe_unretained) id<SessionCellDelegate> delegate;
 
 @end
 
@@ -41,7 +41,7 @@ CGFloat tabSwitcherLocalSessionCellTopBarHeight();
 
 // Returns the top bar of the cell. The top bar holds the favicon and the tab
 // title.
-@property(nonatomic, readonly) UIView* topBar;
+@property(unsafe_unretained, nonatomic, readonly) UIView* topBar;
 
 // Sets the cell's appearance using information in |tab|.
 // The delegate needs to be set before calling this method.

ios/chrome/browser/ui/tab_switcher/tab_switcher_panel_collection_view_layout.mm

@@ -7,7 +7,10 @@
 #include <algorithm>
 
 #include "base/logging.h"
-#include "base/mac/scoped_nsobject.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
 
 namespace {
 const CGFloat minWidthOfTab = 200;
@@ -20,8 +23,8 @@ const CGFloat kMaxCellHeightWidthRatio = 1.8;
 
 @implementation TabSwitcherPanelCollectionViewLayout {
   // Keeps track of the inserted and deleted index paths.
-  base::scoped_nsobject<NSMutableArray> _deletedIndexPaths;
-  base::scoped_nsobject<NSMutableArray> _insertedIndexPaths;
+  NSMutableArray* _deletedIndexPaths;
+  NSMutableArray* _insertedIndexPaths;
 }
 
 - (int)maxRowCountWithColumnCount:(int)columnCount inBounds:(CGSize)boundsSize {

ios/chrome/browser/ui/tab_switcher/tab_switcher_panel_controller.h

@@ -50,8 +50,9 @@ class ChromeBrowserState;
 
 @interface TabSwitcherPanelController : NSObject
 
-@property(nonatomic, readonly) TabSwitcherPanelView* view;
-@property(nonatomic, assign) id<TabSwitcherPanelControllerDelegate> delegate;
+@property(unsafe_unretained, nonatomic, readonly) TabSwitcherPanelView* view;
+@property(nonatomic, unsafe_unretained) id<TabSwitcherPanelControllerDelegate>
+    delegate;
 @property(nonatomic, readonly) TabSwitcherSessionType sessionType;
 
 // Initializes a controller for a view showing local tabs. |offTheRecord|

ios/chrome/browser/ui/tab_switcher/tab_switcher_panel_controller.mm

@@ -6,7 +6,6 @@
 
 #include "base/logging.h"
 #import "base/mac/foundation_util.h"
-#import "base/mac/scoped_nsobject.h"
 #include "base/strings/sys_string_conversions.h"
 #import "ios/chrome/browser/tabs/tab.h"
 #include "ios/chrome/browser/ui/ntp/recent_tabs/synced_sessions.h"
@@ -16,6 +15,10 @@
 #import "ios/chrome/browser/ui/tab_switcher/tab_switcher_panel_view.h"
 #include "ios/chrome/browser/ui/tab_switcher/tab_switcher_session_changes.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 
 void FillVectorWithHashesUsingDistantSession(
@@ -34,12 +37,12 @@ void FillVectorWithHashesUsingDistantSession(
                                          UICollectionViewDelegate,
                                          SessionCellDelegate> {
   ios::ChromeBrowserState* _browserState;  // Weak.
-  base::scoped_nsobject<TabSwitcherPanelView> _panelView;
-  base::scoped_nsobject<TabSwitcherModel> _model;
+  TabSwitcherPanelView* _panelView;
+  TabSwitcherModel* _model;
   std::string _sessionTag;
   TabSwitcherSessionType _sessionType;
-  base::scoped_nsobject<TabSwitcherCache> _cache;
-  base::scoped_nsobject<TabSwitcherPanelOverlayView> _overlayView;
+  TabSwitcherCache* _cache;
+  TabSwitcherPanelOverlayView* _overlayView;
   std::unique_ptr<const synced_sessions::DistantSession> _distantSession;
   std::unique_ptr<const TabModelSnapshot> _localSession;
 }
@@ -61,7 +64,7 @@ void FillVectorWithHashesUsingDistantSession(
   if (self) {
     DCHECK(model);
     _sessionType = TabSwitcherSessionType::DISTANT_SESSION;
-    _model.reset([model retain]);
+    _model = model;
     _distantSession = [model distantSessionForTag:sessionTag];
     _sessionTag = sessionTag;
     _browserState = browserState;
@@ -78,9 +81,9 @@ void FillVectorWithHashesUsingDistantSession(
   if (self) {
     DCHECK(model);
     _sessionType = sessionType;
-    _model.reset([model retain]);
+    _model = model;
     _localSession = [model tabModelSnapshotForLocalSession:sessionType];
-    _cache.reset([cache retain]);
+    _cache = cache;
     _browserState = browserState;
     [self loadView];
   }
@@ -311,9 +314,9 @@ void FillVectorWithHashesUsingDistantSession(
   DCHECK(TabSwitcherSessionTypeIsLocalSession(_sessionType));
 
   if (!_overlayView) {
-    _overlayView.reset([[TabSwitcherPanelOverlayView alloc]
-        initWithFrame:[_panelView bounds]
-         browserState:_browserState]);
+    _overlayView =
+        [[TabSwitcherPanelOverlayView alloc] initWithFrame:[_panelView bounds]
+                                              browserState:_browserState];
     [_overlayView
         setOverlayType:
             (_sessionType == TabSwitcherSessionType::OFF_THE_RECORD_SESSION)
@@ -339,10 +342,9 @@ void FillVectorWithHashesUsingDistantSession(
 }
 
 - (void)loadView {
-  _panelView.reset(
-      [[TabSwitcherPanelView alloc] initWithSessionType:_sessionType]);
-  _panelView.get().collectionView.dataSource = self;
-  _panelView.get().collectionView.delegate = self;
+  _panelView = [[TabSwitcherPanelView alloc] initWithSessionType:_sessionType];
+  _panelView.collectionView.dataSource = self;
+  _panelView.collectionView.delegate = self;
 }
 
 - (synced_sessions::DistantSession const*)distantSession {

ios/chrome/browser/ui/tab_switcher/tab_switcher_panel_view.mm

@@ -4,14 +4,16 @@
 
 #import "ios/chrome/browser/ui/tab_switcher/tab_switcher_panel_view.h"
 
-#import "base/mac/scoped_nsobject.h"
 #import "ios/chrome/browser/ui/tab_switcher/tab_switcher_panel_cell.h"
 #import "ios/chrome/browser/ui/tab_switcher/tab_switcher_panel_collection_view_layout.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 @interface TabSwitcherPanelView () {
-  base::scoped_nsobject<UICollectionView> _collectionView;
-  base::scoped_nsobject<TabSwitcherPanelCollectionViewLayout>
-      _collectionViewLayout;
+  UICollectionView* _collectionView;
+  TabSwitcherPanelCollectionViewLayout* _collectionViewLayout;
   TabSwitcherSessionType _sessionType;
 }
 
@@ -57,11 +59,10 @@
 #pragma mark - Private
 
 - (void)loadSubviews {
-  _collectionViewLayout.reset(
-      [[TabSwitcherPanelCollectionViewLayout alloc] init]);
-  _collectionView.reset([[UICollectionView alloc]
-             initWithFrame:self.bounds
-      collectionViewLayout:_collectionViewLayout.get()]);
+  _collectionViewLayout = [[TabSwitcherPanelCollectionViewLayout alloc] init];
+  _collectionView =
+      [[UICollectionView alloc] initWithFrame:self.bounds
+                         collectionViewLayout:_collectionViewLayout];
   if (_sessionType == TabSwitcherSessionType::DISTANT_SESSION) {
     [_collectionView registerClass:[TabSwitcherDistantSessionCell class]
         forCellWithReuseIdentifier:[TabSwitcherDistantSessionCell identifier]];

ios/chrome/browser/ui/tab_switcher/tab_switcher_session_cell_data.mm

@@ -6,6 +6,10 @@
 #include "ios/chrome/grit/ios_strings.h"
 #include "ui/base/l10n/l10n_util.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 @implementation TabSwitcherSessionCellData
 
 @synthesize type = _type;

ios/chrome/browser/ui/tab_switcher/tab_switcher_session_changes.mm

@@ -6,6 +6,10 @@
 
 #import "ios/chrome/browser/ui/tab_switcher/tab_switcher_utils.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 TabSwitcherSessionChanges::TabSwitcherSessionChanges(
     std::vector<size_t> const& tabHashesInInitialState,
     std::vector<size_t> const& tabHashesInFinalState) {

ios/chrome/browser/ui/tab_switcher/tab_switcher_tab_strip_placeholder_view.mm

@@ -8,11 +8,13 @@
 
 #import <QuartzCore/QuartzCore.h>
 
-#import "base/ios/weak_nsobject.h"
 #include "base/mac/foundation_util.h"
-#include "base/mac/scoped_nsobject.h"
 #include "ios/chrome/browser/ui/rtl_geometry.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 // Returns the animation drag coefficient set by the iPhone simulator.
 // This is useful when debugging with the simulator because when
 // "slow animation" mode is toggled, it only impacts UIKit animations not
@@ -106,16 +108,15 @@ const CGFloat kTabFoldAnimationDuration = 0.15;
   _animatingFold = YES;
   [self setUserInteractionEnabled:NO];
   [CATransaction begin];
-  base::WeakNSObject<TabSwitcherTabStripPlaceholderView> weakSelf(self);
+  __weak TabSwitcherTabStripPlaceholderView* weakSelf = self;
   [CATransaction setCompletionBlock:^{
-    base::scoped_nsobject<TabSwitcherTabStripPlaceholderView> strongSelf(
-        [weakSelf retain]);
+    TabSwitcherTabStripPlaceholderView* strongSelf = weakSelf;
     if (!strongSelf) {
       if (completion)
         completion();
       return;
     }
-    strongSelf.get()->_animatingFold = NO;
+    strongSelf->_animatingFold = NO;
     [strongSelf setUserInteractionEnabled:YES];
     if (completion)
       completion();

ios/chrome/browser/ui/tab_switcher/tab_switcher_transition_context.mm

@@ -4,7 +4,6 @@
 
 #include "ios/chrome/browser/ui/tab_switcher/tab_switcher_transition_context.h"
 
-#include "base/mac/objc_property_releaser.h"
 #import "ios/chrome/browser/tabs/tab.h"
 #import "ios/chrome/browser/ui/browser_view_controller.h"
 #include "ios/chrome/browser/ui/tab_switcher/tab_switcher_transition_context.h"
@@ -12,25 +11,26 @@
 #import "ios/chrome/browser/ui/tabs/tab_strip_controller.h"
 #import "ios/chrome/browser/ui/uikit_ui_util.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 @class BrowserViewController;
 
 @interface TabSwitcherTransitionContextContent () {
-  base::scoped_nsobject<TabSwitcherTabStripPlaceholderView>
-      _tabStripPlaceholderView;
-  base::WeakNSObject<BrowserViewController> _bvc;
+  TabSwitcherTabStripPlaceholderView* _tabStripPlaceholderView;
+  __weak BrowserViewController* _bvc;
 }
 
 @end
 
 @implementation TabSwitcherTransitionContextContent {
-  base::mac::ObjCPropertyReleaser
-      _propertyReleaser_tabSwitcherTransitionContextContent;
 }
 
 + (instancetype)tabSwitcherTransitionContextContentFromBVC:
     (BrowserViewController*)bvc {
   TabSwitcherTransitionContextContent* transitionContextContent =
-      [[[TabSwitcherTransitionContextContent alloc] init] autorelease];
+      [[TabSwitcherTransitionContextContent alloc] init];
 
   transitionContextContent.initialTabID = bvc.tabModel.currentTab.tabId;
 
@@ -40,17 +40,16 @@
   }
 
   UIView* toolbarView = [[bvc toolbarController] view];
-  base::scoped_nsobject<UIView> toolbarSnapshotView;
+  UIView* toolbarSnapshotView;
   if ([toolbarView window]) {
-    toolbarSnapshotView.reset(
-        [[toolbarView snapshotViewAfterScreenUpdates:NO] retain]);
+    toolbarSnapshotView = [toolbarView snapshotViewAfterScreenUpdates:NO];
   } else {
-    toolbarSnapshotView.reset([[UIView alloc] initWithFrame:toolbarView.frame]);
+    toolbarSnapshotView = [[UIView alloc] initWithFrame:toolbarView.frame];
     [toolbarSnapshotView layer].contents = static_cast<id>(
         CaptureViewWithOption(toolbarView, 1, kClientSideRendering).CGImage);
   }
   transitionContextContent.toolbarSnapshotView = toolbarSnapshotView;
-  transitionContextContent->_bvc.reset(bvc);
+  transitionContextContent->_bvc = bvc;
   return transitionContextContent;
 }
 
@@ -65,8 +64,6 @@
 - (instancetype)init {
   self = [super init];
   if (self) {
-    _propertyReleaser_tabSwitcherTransitionContextContent.Init(
-        self, [TabSwitcherTransitionContextContent class]);
   }
   return self;
 }
@@ -74,8 +71,6 @@
 @end
 
 @implementation TabSwitcherTransitionContext {
-  base::mac::ObjCPropertyReleaser
-      _propertyReleaser_tabSwitcherTransitionContext;
 }
 
 + (instancetype)
@@ -83,7 +78,7 @@ tabSwitcherTransitionContextWithCurrent:(BrowserViewController*)currentBVC
                                 mainBVC:(BrowserViewController*)mainBVC
                                  otrBVC:(BrowserViewController*)otrBVC {
   TabSwitcherTransitionContext* transitionContext =
-      [[[TabSwitcherTransitionContext alloc] init] autorelease];
+      [[TabSwitcherTransitionContext alloc] init];
   Tab* currentTab = [[currentBVC tabModel] currentTab];
   UIImage* tabSnapshotImage =
       [currentTab generateSnapshotWithOverlay:YES visibleFrameOnly:YES];
@@ -108,8 +103,6 @@ tabSwitcherTransitionContextWithCurrent:(BrowserViewController*)currentBVC
 - (instancetype)init {
   self = [super init];
   if (self) {
-    _propertyReleaser_tabSwitcherTransitionContext.Init(
-        self, [TabSwitcherTransitionContext class]);
   }
   return self;
 }

ios/chrome/browser/ui/tab_switcher/tab_switcher_view.h

@@ -28,10 +28,11 @@ enum NewTabButtonStyle { UNINITIALIZED, BLUE, GRAY, HIDDEN };
 
 @interface TabSwitcherView : UIView<UIScrollViewDelegate>
 
-@property(nonatomic, readonly) TabSwitcherHeaderView* headerView;
-@property(nonatomic, readonly) UIScrollView* scrollView;
+@property(unsafe_unretained, nonatomic, readonly)
+    TabSwitcherHeaderView* headerView;
+@property(unsafe_unretained, nonatomic, readonly) UIScrollView* scrollView;
 
-@property(nonatomic, assign) id<TabSwitcherViewDelegate> delegate;
+@property(nonatomic, unsafe_unretained) id<TabSwitcherViewDelegate> delegate;
 
 // Select the panel at the given index, updating both the header and content.
 // The panel selection will be animated if VoiceOver is disabled.

ios/chrome/browser/ui/tab_switcher/tab_switcher_view.mm

@@ -6,7 +6,6 @@
 
 #include "base/logging.h"
 #include "base/mac/foundation_util.h"
-#include "base/mac/scoped_nsobject.h"
 #include "base/metrics/user_metrics.h"
 #import "ios/chrome/browser/ui/colors/MDCPalette+CrAdditions.h"
 #include "ios/chrome/browser/ui/rtl_geometry.h"
@@ -19,6 +18,10 @@
 #import "ios/third_party/material_components_ios/src/components/Palettes/src/MaterialPalettes.h"
 #include "ui/base/l10n/l10n_util.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 const CGFloat kHeaderHeight = 95;
 const CGFloat kNewTabButtonMarginFromEdges = 48;
@@ -26,10 +29,10 @@ const CGFloat kNewTabButtonWidth = 48;
 }
 
 @interface TabSwitcherView ()<UIScrollViewDelegate> {
-  base::scoped_nsobject<TabSwitcherHeaderView> _headerView;
-  base::scoped_nsobject<UIScrollView> _scrollView;
-  base::scoped_nsobject<MDCButton> _openNewTabButton;
-  base::scoped_nsobject<NSMutableArray> _panels;
+  TabSwitcherHeaderView* _headerView;
+  UIScrollView* _scrollView;
+  MDCButton* _openNewTabButton;
+  NSMutableArray* _panels;
   ios_internal::NewTabButtonStyle _openNewTabButtonStyle;
   NSInteger _previousPanelIndex;
 }
@@ -61,7 +64,7 @@ const CGFloat kNewTabButtonWidth = 48;
   if (self) {
     _openNewTabButtonStyle = ios_internal::NewTabButtonStyle::UNINITIALIZED;
     [self loadSubviews];
-    _panels.reset([[NSMutableArray alloc] init]);
+    _panels = [[NSMutableArray alloc] init];
     _previousPanelIndex = -1;
   }
   return self;
@@ -104,7 +107,7 @@ const CGFloat kNewTabButtonWidth = 48;
 }
 
 - (void)removePanelViewAtIndex:(NSUInteger)index updateScrollView:(BOOL)update {
-  DCHECK_EQ([[_panels objectAtIndex:index] superview], _scrollView.get());
+  DCHECK_EQ([[_panels objectAtIndex:index] superview], _scrollView);
   [[_panels objectAtIndex:index] removeFromSuperview];
   [_panels removeObjectAtIndex:index];
   if (update)
@@ -171,14 +174,14 @@ const CGFloat kNewTabButtonWidth = 48;
 
 - (void)loadSubviews {
   // Creates and add the header view showing the list of panels.
-  base::scoped_nsobject<TabSwitcherHeaderView> headerView(
-      [[TabSwitcherHeaderView alloc] initWithFrame:[self headerViewFrame]]);
+  TabSwitcherHeaderView* headerView =
+      [[TabSwitcherHeaderView alloc] initWithFrame:[self headerViewFrame]];
   [self addSubview:headerView];
   _headerView = headerView;
 
   // Creates and add the scrollview containing the panels.
-  base::scoped_nsobject<UIScrollView> scrollView(
-      [[UIScrollView alloc] initWithFrame:[self scrollViewFrame]]);
+  UIScrollView* scrollView =
+      [[UIScrollView alloc] initWithFrame:[self scrollViewFrame]];
   [scrollView setBackgroundColor:[[MDCPalette greyPalette] tint900]];
   [scrollView setAlwaysBounceHorizontal:YES];
   [scrollView setDelegate:self];
@@ -190,7 +193,7 @@ const CGFloat kNewTabButtonWidth = 48;
   _scrollView = scrollView;
 
   // Creates and add the floating new tab button.
-  _openNewTabButton.reset([[MDCFloatingButton alloc] init]);
+  _openNewTabButton = [[MDCFloatingButton alloc] init];
   UIImage* openNewTabButtonImage =
       [[UIImage imageNamed:@"tabswitcher_new_tab_fab"]
           imageWithRenderingMode:UIImageRenderingModeAlwaysTemplate];