Prevent bookmark scroll position from mistakenly reset to zero.

In bookmark_home_handset_view_controller and
bookmark_home_tablet_ntp_controller, prevent primaryView's content
position from mistakenly reset to zero at viewWillLayoutSubviews().

Bug: 608777
Change-Id: Ifa6a4c075866509171180614cd0d5916a30a9466
Reviewed-on: https://chromium-review.googlesource.com/578693
Commit-Queue: Marti Wong <martiw@chromium.org>
Reviewed-by: Eric Noyau <noyau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#488617}

ios/chrome/browser/ui/bookmarks/bookmark_collection_view.mm

@@ -255,7 +255,7 @@ const NSTimeInterval kShowEmptyBookmarksBackgroundRefreshDelay = 1.0;
     return self.collectionView.contentOffset.y;
 
   // In short landscape mode and portrait mode, there are 2 cells per row.
-  if ([self wideLandscapeMode])
+  if (![self wideLandscapeMode])
     return self.collectionView.contentOffset.y;
 
   // In wide landscape mode, there are 3 cells per row.

ios/chrome/browser/ui/bookmarks/bookmark_home_handset_view_controller.mm

@@ -130,15 +130,20 @@ using bookmarks::BookmarkNode;
   [super viewWillAppear:animated];
   UIInterfaceOrientation orient = GetInterfaceOrientation();
   [self updateUIForInterfaceOrientation:orient duration:0];
-  if (self.cachedContentPosition) {
-    [self.folderView
-        applyContentPosition:[self.cachedContentPosition floatValue]];
-    self.cachedContentPosition = nil;
-  }
 }
 
 - (void)viewWillLayoutSubviews {
   [super viewWillLayoutSubviews];
+
+  // Store the content scroll position.
+  CGFloat contentPosition =
+      [[self folderView] contentPositionInPortraitOrientation];
+  // If we have the cached position, use it instead.
+  if (self.cachedContentPosition) {
+    contentPosition = [self.cachedContentPosition floatValue];
+    self.cachedContentPosition = nil;
+  }
+
   // Invalidate the layout of the collection view, as its frame might have
   // changed. Normally, this can be done automatically when the collection view
   // layout returns YES to -shouldInvalidateLayoutForBoundsChange:.
@@ -151,6 +156,14 @@ using bookmarks::BookmarkNode;
   self.navigationBar.frame = [self navigationBarFrame];
   self.editingBar.frame = [self navigationBarFrame];
   [self.panelView setFrame:[self frameForPanelView]];
+
+  // Restore the content scroll position if it was reset to zero. This could
+  // happen when folderView is newly created (restore from cached) or its frame
+  // height has changed.
+  if (contentPosition > 0 &&
+      [[self folderView] contentPositionInPortraitOrientation] == 0) {
+    [[self folderView] applyContentPosition:contentPosition];
+  }
 }
 
 - (BOOL)prefersStatusBarHidden {

ios/chrome/browser/ui/bookmarks/bookmark_home_tablet_ntp_controller.mm

@@ -57,10 +57,9 @@ const CGFloat kNavigationBarTopMargin = 8.0;
 @interface BookmarkHomeTabletNTPController ()<BookmarkMenuViewDelegate>
 
 // When the view is first shown on the screen, this property represents the
-// cached value of the y of the content offset of the primary view. This
+// cached value of the y of the content offset of the folder view. This
 // property is set to nil after it is used.
-@property(nonatomic, strong)
-    NSNumber* cachedContentPosition;  // FIXME: INACTIVE
+@property(nonatomic, strong) NSNumber* cachedContentPosition;
 
 #pragma mark Private methods
 
@@ -99,6 +98,16 @@ const CGFloat kNavigationBarTopMargin = 8.0;
 
 - (void)viewWillLayoutSubviews {
   [super viewWillLayoutSubviews];
+
+  // Store the content scroll position.
+  CGFloat contentPosition =
+      [[self folderView] contentPositionInPortraitOrientation];
+  // If we have the cached position, use it instead.
+  if (self.cachedContentPosition) {
+    contentPosition = [self.cachedContentPosition floatValue];
+    self.cachedContentPosition = nil;
+  }
+
   if (!self.folderView && ![self primaryMenuItem] && self.bookmarks->loaded()) {
     BookmarkMenuItem* item = nil;
     CGFloat position = 0;
@@ -132,6 +141,14 @@ const CGFloat kNavigationBarTopMargin = 8.0;
   [self updateNavigationBarWithDuration:0 orientation:orient];
   if (![self shouldPresentMenuInSlideInPanel])
     [self updateMenuViewLayout];
+
+  // Restore the content scroll position if it was reset to zero. This could
+  // happen when folderView is newly created (restore from cached); its frame
+  // height has changed; or it was re-attached to the view hierarchy.
+  if (contentPosition > 0 &&
+      [[self folderView] contentPositionInPortraitOrientation] == 0) {
+    [[self folderView] applyContentPosition:contentPosition];
+  }
 }
 
 - (void)viewDidLoad {