[ios] Enables an experiment for presenting BVC and the stack view.

These view controllers are currently contained children of MainViewController.
When the experiment is enabled, they are presented instead.

This CL also adds a completion handler to [MainViewController
setActiveViewController:completion:].  This handler will be used in a future CL.

BUG=768563

Change-Id: Iefead6de0a1471dcd07c67d634acbab15c70b9c3
Reviewed-on: https://chromium-review.googlesource.com/683196Reviewed-by: edchin <edchin@chromium.org>
Commit-Queue: Rohit Rao (ping after 24h) <rohitrao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#504451}

ios/chrome/app/main_controller.mm

@@ -1742,7 +1742,8 @@ const int kExternalFilesCleanupDelaySeconds = 60;
 }
 
 - (void)displayCurrentBVC {
-  self.mainViewController.activeViewController = self.currentBVC;
+  [self.mainViewController setActiveViewController:self.currentBVC
+                                        completion:nil];
 }
 
 - (TabModel*)currentTabModel {
@@ -1806,12 +1807,14 @@ const int kExternalFilesCleanupDelaySeconds = 60;
                                             mainBVC:self.mainBVC
                                              otrBVC:self.otrBVC];
     [_tabSwitcherController setTransitionContext:transitionContext];
-    self.mainViewController.activeViewController = _tabSwitcherController;
+    [self.mainViewController setActiveViewController:_tabSwitcherController
+                                          completion:nil];
     [_tabSwitcherController showWithSelectedTabAnimation];
   } else {
     // User interaction is disabled when the stack controller is dismissed.
     [[_tabSwitcherController view] setUserInteractionEnabled:YES];
-    self.mainViewController.activeViewController = _tabSwitcherController;
+    [self.mainViewController setActiveViewController:_tabSwitcherController
+                                          completion:nil];
     [_tabSwitcherController showWithSelectedTabAnimation];
   }
 }

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

@@ -14,6 +14,7 @@ source_set("main") {
     "main_view_controller.mm",
   ]
   deps = [
+    ":feature_flags",
     "//base",
     "//ios/chrome/browser",
     "//ios/chrome/browser/browser_state",
@@ -54,13 +55,16 @@ source_set("unit_tests") {
     "main_view_controller_unittest.mm",
   ]
   deps = [
+    ":feature_flags",
     ":main",
     "//base",
+    "//base/test:test_support",
     "//components/bookmarks/test",
     "//ios/chrome/browser/bookmarks",
     "//ios/chrome/browser/browser_state:test_support",
     "//ios/chrome/browser/tabs",
     "//ios/chrome/browser/ui:ui_internal",
+    "//ios/chrome/test:block_cleanup_test",
     "//ios/web/public/test",
     "//testing/gtest",
   ]

ios/chrome/browser/ui/main/main_view_controller.h

@@ -7,12 +7,21 @@
 
 #import <UIKit/UIKit.h>
 
+#import "base/ios/block_types.h"
+
 // A UIViewController that provides a property to maintain a single child view
 // controller.
 @interface MainViewController : UIViewController
-// The child view controller, if any, that is active. Assigning to
-// |activeViewController| will remove any previous active view controller.
-@property(nonatomic, strong) UIViewController* activeViewController;
+
+// The view controller, if any, that is active.
+@property(nonatomic, readonly, strong) UIViewController* activeViewController;
+
+// Sets the active view controller, replacing any previously-active view
+// controller.  The |completion| block is invoked once the new view controller
+// is presented or added as a child.
+- (void)setActiveViewController:(UIViewController*)activeViewController
+                     completion:(ProceduralBlock)completion;
+
 @end
 
 #endif  // IOS_CHROME_BROWSER_UI_MAIN_MAIN_VIEW_CONTROLLER_H_

ios/chrome/browser/ui/main/main_view_controller.mm

@@ -5,6 +5,7 @@
 #import "ios/chrome/browser/ui/main/main_view_controller.h"
 
 #import "base/logging.h"
+#include "ios/chrome/browser/ui/main/main_feature_flags.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
@@ -13,10 +14,15 @@
 @implementation MainViewController
 
 - (UIViewController*)activeViewController {
-  return [self.childViewControllers firstObject];
+  if (TabSwitcherPresentsBVCEnabled()) {
+    return self.presentedViewController;
+  } else {
+    return [self.childViewControllers firstObject];
+  }
 }
 
-- (void)setActiveViewController:(UIViewController*)activeViewController {
+- (void)setActiveViewController:(UIViewController*)activeViewController
+                     completion:(void (^)())completion {
   DCHECK(activeViewController);
   if (self.activeViewController == activeViewController)
     return;
@@ -24,27 +30,54 @@
   // TODO(crbug.com/546189): DCHECK here that there isn't a modal view
   // controller showing once the known violations of that are fixed.
 
-  // Remove the current active view controller, if any.
-  if (self.activeViewController) {
-    [self.activeViewController willMoveToParentViewController:nil];
-    [self.activeViewController.view removeFromSuperview];
-    [self.activeViewController removeFromParentViewController];
+  if (TabSwitcherPresentsBVCEnabled()) {
+    if (self.activeViewController) {
+      // This call must be to super, as the override of
+      // dismissViewControllerAnimated:completion: below tries to dismiss using
+      // self.activeViewController, but this call explicitly needs to present
+      // using the MainViewController itself.
+      [super dismissViewControllerAnimated:NO completion:nil];
+    }
+
+    // This call must be to super, as the override of
+    // presentViewController:animated:completion: below tries to present using
+    // self.activeViewController, but this call explicitly needs to present
+    // using the MainViewController itself.
+    [super
+        presentViewController:activeViewController
+                     animated:NO
+                   completion:^{
+                     DCHECK(self.activeViewController == activeViewController);
+                     if (completion) {
+                       completion();
+                     }
+                   }];
+  } else {
+    // Remove the current active view controller, if any.
+    if (self.activeViewController) {
+      [self.activeViewController willMoveToParentViewController:nil];
+      [self.activeViewController.view removeFromSuperview];
+      [self.activeViewController removeFromParentViewController];
+    }
+
+    DCHECK(self.activeViewController == nil);
+    DCHECK(self.view.subviews.count == 0);
+
+    // Add the new active view controller.
+    [self addChildViewController:activeViewController];
+    self.activeViewController.view.frame = self.view.bounds;
+    [self.view addSubview:self.activeViewController.view];
+    [activeViewController didMoveToParentViewController:self];
+
+    // Let the system know that the child has changed so appearance updates can
+    // be made.
+    [self setNeedsStatusBarAppearanceUpdate];
+
+    DCHECK(self.activeViewController == activeViewController);
+    if (completion) {
+      completion();
+    }
   }
-
-  DCHECK(self.activeViewController == nil);
-  DCHECK(self.view.subviews.count == 0);
-
-  // Add the new active view controller.
-  [self addChildViewController:activeViewController];
-  self.activeViewController.view.frame = self.view.bounds;
-  [self.view addSubview:self.activeViewController.view];
-  [activeViewController didMoveToParentViewController:self];
-
-  // Let the system know that the child has changed so appearance updates can
-  // be made.
-  [self setNeedsStatusBarAppearanceUpdate];
-
-  DCHECK(self.activeViewController == activeViewController);
 }
 
 #pragma mark - UIViewController methods

ios/chrome/browser/ui/main/main_view_controller_unittest.mm

@@ -6,6 +6,10 @@
 
 #import <UIKit/UIKit.h>
 
+#import "base/test/ios/wait_util.h"
+#include "base/test/scoped_feature_list.h"
+#include "ios/chrome/browser/ui/main/main_feature_flags.h"
+#import "ios/chrome/test/block_cleanup_test.h"
 #include "testing/gtest_mac.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
@@ -52,7 +56,40 @@
 
 namespace {
 
-TEST(MainViewControllerTest, ActiveVC) {
+class MainViewControllerTest : public BlockCleanupTest {
+ public:
+  MainViewControllerTest() = default;
+  ~MainViewControllerTest() override = default;
+
+  void TearDown() override {
+    if (original_root_view_controller_) {
+      [[UIApplication sharedApplication] keyWindow].rootViewController =
+          original_root_view_controller_;
+      original_root_view_controller_ = nil;
+    }
+  }
+
+  // Sets the current key window's rootViewController and saves a pointer to
+  // the original VC to allow restoring it at the end of the test.
+  void SetRootViewController(UIViewController* new_root_view_controller) {
+    original_root_view_controller_ =
+        [[[UIApplication sharedApplication] keyWindow] rootViewController];
+    [[UIApplication sharedApplication] keyWindow].rootViewController =
+        new_root_view_controller;
+  }
+
+ private:
+  // The key window's original root view controller, which must be restored at
+  // the end of the test.
+  UIViewController* original_root_view_controller_;
+
+  DISALLOW_COPY_AND_ASSIGN(MainViewControllerTest);
+};
+
+TEST_F(MainViewControllerTest, ActiveVC) {
+  base::test::ScopedFeatureList disable_feature;
+  disable_feature.InitAndDisableFeature(kTabSwitcherPresentsBVC);
+
   MainViewController* main_view_controller = [[MainViewController alloc] init];
   UIViewController* child_view_controller_1 = [[UIViewController alloc] init];
   UIViewController* child_view_controller_2 = [[UIViewController alloc] init];
@@ -71,7 +108,10 @@ TEST(MainViewControllerTest, ActiveVC) {
             [main_view_controller activeViewController]);
 }
 
-TEST(MainViewControllerTest, SetActiveVC) {
+TEST_F(MainViewControllerTest, SetActiveVCWithContainment) {
+  base::test::ScopedFeatureList disable_feature;
+  disable_feature.InitAndDisableFeature(kTabSwitcherPresentsBVC);
+
   MainViewController* main_view_controller = [[MainViewController alloc] init];
   CGRect windowRect = CGRectMake(0, 0, 200, 200);
   [main_view_controller view].frame = windowRect;
@@ -80,7 +120,8 @@ TEST(MainViewControllerTest, SetActiveVC) {
       [[MockViewController alloc] init];
   [child_view_controller_1 view].frame = CGRectMake(0, 0, 10, 10);
 
-  [main_view_controller setActiveViewController:child_view_controller_1];
+  [main_view_controller setActiveViewController:child_view_controller_1
+                                     completion:nil];
   EXPECT_EQ(child_view_controller_1,
             [[main_view_controller childViewControllers] firstObject]);
   EXPECT_EQ([child_view_controller_1 view],
@@ -97,7 +138,8 @@ TEST(MainViewControllerTest, SetActiveVC) {
             [child_view_controller_1 willMoveToParentViewControllerArgument]);
 
   UIViewController* child_view_controller_2 = [[UIViewController alloc] init];
-  [main_view_controller setActiveViewController:child_view_controller_2];
+  [main_view_controller setActiveViewController:child_view_controller_2
+                                     completion:nil];
   EXPECT_EQ(child_view_controller_2,
             [[main_view_controller childViewControllers] firstObject]);
   EXPECT_EQ(1U, [[main_view_controller childViewControllers] count]);
@@ -112,18 +154,18 @@ TEST(MainViewControllerTest, SetActiveVC) {
             [child_view_controller_1 didMoveToParentViewControllerArgument]);
 }
 
-TEST(MainViewControllerTest, StatusBar) {
+TEST_F(MainViewControllerTest, StatusBar) {
+  base::test::ScopedFeatureList disable_feature;
+  disable_feature.InitAndDisableFeature(kTabSwitcherPresentsBVC);
+
   MainViewController* main_view_controller = [[MainViewController alloc] init];
-  // MVC needs to be the root view controller for this to work, so save the
-  // current one and restore it at the end of the test.
-  UIViewController* root_view_controller =
-      [[[UIApplication sharedApplication] keyWindow] rootViewController];
-  [[UIApplication sharedApplication] keyWindow].rootViewController =
-      main_view_controller;
+  SetRootViewController(main_view_controller);
+
   UIViewController* status_bar_visible_view_controller =
       [[UIViewController alloc] init];
   [main_view_controller
-      setActiveViewController:status_bar_visible_view_controller];
+      setActiveViewController:status_bar_visible_view_controller
+                   completion:nil];
   // Check if the status bar is hidden by testing if the status bar rect is
   // CGRectZero.
   EXPECT_FALSE(CGRectEqualToRect(
@@ -131,13 +173,101 @@ TEST(MainViewControllerTest, StatusBar) {
   HiddenStatusBarViewController* status_bar_hidden_view_controller =
       [[HiddenStatusBarViewController alloc] init];
   [main_view_controller
-      setActiveViewController:status_bar_hidden_view_controller];
+      setActiveViewController:status_bar_hidden_view_controller
+                   completion:nil];
   EXPECT_EQ([main_view_controller childViewControllerForStatusBarHidden],
             status_bar_hidden_view_controller);
   EXPECT_TRUE(CGRectEqualToRect(
       [UIApplication sharedApplication].statusBarFrame, CGRectZero));
-  [[UIApplication sharedApplication] keyWindow].rootViewController =
-      root_view_controller;
+}
+
+// Tests that completion handlers are called properly after the new view
+// controller is made active, when using containment
+TEST_F(MainViewControllerTest, CompletionHandlersWithContainment) {
+  base::test::ScopedFeatureList disable_feature;
+  disable_feature.InitAndDisableFeature(kTabSwitcherPresentsBVC);
+
+  MainViewController* main_view_controller = [[MainViewController alloc] init];
+  CGRect windowRect = CGRectMake(0, 0, 200, 200);
+  [main_view_controller view].frame = windowRect;
+
+  UIViewController* child_view_controller_1 = [[UIViewController alloc] init];
+  [child_view_controller_1 view].frame = CGRectMake(0, 0, 10, 10);
+
+  UIViewController* child_view_controller_2 = [[UIViewController alloc] init];
+  [child_view_controller_2 view].frame = CGRectMake(20, 20, 10, 10);
+
+  // Tests that the completion handler is called when there is no preexisting
+  // active view controller.
+  __block BOOL completion_handler_was_called = false;
+  [main_view_controller setActiveViewController:child_view_controller_1
+                                     completion:^{
+                                       completion_handler_was_called = YES;
+                                     }];
+  base::test::ios::WaitUntilCondition(^bool() {
+    return completion_handler_was_called;
+  });
+  ASSERT_TRUE(completion_handler_was_called);
+
+  // Tests that the completion handler is called when replacing an existing
+  // active view controller.
+  completion_handler_was_called = NO;
+  [main_view_controller setActiveViewController:child_view_controller_2
+                                     completion:^{
+                                       completion_handler_was_called = YES;
+                                     }];
+  base::test::ios::WaitUntilCondition(^bool() {
+    return completion_handler_was_called;
+  });
+  ASSERT_TRUE(completion_handler_was_called);
+}
+
+// Tests that setting the active view controller work and that completion
+// handlers are called properly after the new view controller is made active,
+// when using presentation.
+TEST_F(MainViewControllerTest,
+       SetActiveVCAndCompletionHandlersWithPresentation) {
+  base::test::ScopedFeatureList enable_feature;
+  enable_feature.InitAndEnableFeature(kTabSwitcherPresentsBVC);
+
+  MainViewController* main_view_controller = [[MainViewController alloc] init];
+  SetRootViewController(main_view_controller);
+  CGRect windowRect = CGRectMake(0, 0, 200, 200);
+  [main_view_controller view].frame = windowRect;
+
+  UIViewController* child_view_controller_1 = [[UIViewController alloc] init];
+  [child_view_controller_1 view].frame = CGRectMake(0, 0, 10, 10);
+
+  UIViewController* child_view_controller_2 = [[UIViewController alloc] init];
+  [child_view_controller_2 view].frame = CGRectMake(20, 20, 10, 10);
+
+  // Tests that the completion handler is called when there is no preexisting
+  // active view controller.
+  __block BOOL completion_handler_was_called = false;
+  [main_view_controller setActiveViewController:child_view_controller_1
+                                     completion:^{
+                                       completion_handler_was_called = YES;
+                                     }];
+  base::test::ios::WaitUntilCondition(^bool() {
+    return completion_handler_was_called;
+  });
+  ASSERT_TRUE(completion_handler_was_called);
+  EXPECT_EQ(main_view_controller.presentedViewController,
+            child_view_controller_1);
+
+  // Tests that the completion handler is called when replacing an existing
+  // active view controller.
+  completion_handler_was_called = NO;
+  [main_view_controller setActiveViewController:child_view_controller_2
+                                     completion:^{
+                                       completion_handler_was_called = YES;
+                                     }];
+  base::test::ios::WaitUntilCondition(^bool() {
+    return completion_handler_was_called;
+  });
+  ASSERT_TRUE(completion_handler_was_called);
+  EXPECT_EQ(main_view_controller.presentedViewController,
+            child_view_controller_2);
 }
 
 }  // namespace