Use correct snapshot for the tab transition animation on iPad

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

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "ios/chrome/browser/ui/tab_switcher/tab_switcher_controller.h"
 
 #include "base/ios/block_types.h"
 #include "base/ios/weak_nsobject.h"
 #include "base/mac/scoped_nsobject.h"
 #include "base/metrics/user_metrics.h"
@@ skipping 550 matching lines @@
   const CGFloat cellTopBarHeight = tabSwitcherLocalSessionCellTopBarHeight();
   CGRect finalToolbarScreenshotFrame =
       CGRectMake(0, 0, selectedCellFrame.size.width, cellTopBarHeight);
 
   base::scoped_nsobject<UIImageView> tabScreenshotImageView(
       [[UIImageView alloc] initWithFrame:CGRectZero]);
 
   base::WeakNSObject<UIImageView> weakTabScreenshotImageView(
       tabScreenshotImageView.get());
 
-  if (self.transitionContext.initialTabModel != tabModel ||
-      transitionContextContent.initialSelectedTabIndex != selectedTabIndex) {
+  if ([self initialTabModelAndTabIDMatchesTabModel:tabModel
+                                             tabID:selectedTab.tabId]) {
+    tabScreenshotImageView.get().image =
+        self.transitionContext.tabSnapshotImage;
+  } else {
+    // If transitioning to a different tab than the one animated in
+    // from, a new snapshot should be generated instead of using the transition
+    // context
     tabScreenshotImageView.get().image =
         [self updateScreenshotForCellIfNeeded:selectedCell tabModel:tabModel];
     [selectedTab retrieveSnapshot:^(UIImage* snapshot) {
       [weakTabScreenshotImageView setImage:snapshot];
     }];
-  } else {
-    tabScreenshotImageView.get().image =
-        self.transitionContext.tabSnapshotImage;
   }
 
   const CGSize tabScreenshotImageSize = tabScreenshotImageView.get().image.size;
 
   CGRect initialTabScreenshotFrame = CGRectZero;
   const CGSize toolbarSize = toolbarController.view.bounds.size;
   CGSize initialTabTargetSize =
       CGSizeMake(initialTabFrame.size.width,
                  initialTabFrame.size.height - toolbarSize.height);
   CGSize revisedTargetSize = CGSizeZero;
@@ skipping 118 matching lines @@
     tabScreenshotImageView.get().frame = finalTabScreenshotFrame;
   };
 
   [UIView animateWithDuration:animated ? kTransitionAnimationDuration : 0
                         delay:0
                       options:UIViewAnimationCurveEaseInOut
                    animations:animationBlock
                    completion:completionBlock];
 }
 
+- (BOOL)initialTabModelAndTabIDMatchesTabModel:(nonnull TabModel*)tabModel
+                                         tabID:(nonnull NSString*)tabID {
+  TabModel* initialTabModel = self.transitionContext.initialTabModel;
+  NSString* initialTabID =
+      [self transitionContextContentForTabModel:initialTabModel].initialTabID;
+  return initialTabModel == tabModel && [initialTabID isEqualToString:tabID];
+}
+
 - (void)updateLocalPanelsCells {
   auto mainTabPanel =
       [self panelControllerForTabModel:[_tabSwitcherModel mainTabModel]];
   auto otrTabPanel =
       [self panelControllerForTabModel:[_tabSwitcherModel otrTabModel]];
   [mainTabPanel reload];
   [otrTabPanel reload];
 }
 
 - (NSInteger)currentPanelIndex {
@@ skipping 507 matching lines @@
         base::UserMetricsAction("MobileTabSwitcherCloseNonIncognitoTab"));
   }
 }
 
 - (void)tabSwitcherPanelControllerDidUpdateOverlayViewVisibility:
     (TabSwitcherPanelController*)tabSwitcherPanelController {
   [_tabSwitcherView updateOverlayButtonState];
 }
 
 @end