Use correct snapshot for the tab transition animation on iPad

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

 // Copyright 2016 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.
 
 #ifndef IOS_CHROME_BROWSER_UI_TAB_SWITCHER_TAB_SWITCHER_TRANSITION_CONTEXT_H_
 #define IOS_CHROME_BROWSER_UI_TAB_SWITCHER_TAB_SWITCHER_TRANSITION_CONTEXT_H_
 
 #import <UIKit/UIKit.h>
 
 #import "ios/chrome/browser/ui/tab_switcher/tab_switcher_tab_strip_placeholder_view.h"
 
 @class TabModel;
 @class BrowserViewController;
 
 // Holds the informations about a browser view controller that will be used
 // to create the transition from the browser view controller to the tab switcher
 // and vice versa.
 @interface TabSwitcherTransitionContextContent : NSObject
 
 // Create a transition context content from a browser view controller.
 + (instancetype)tabSwitcherTransitionContextContentFromBVC:
     (BrowserViewController*)bvc;
 
 // Returns an autoreleased placeholder representing the BVC's toolbar.
 - (TabSwitcherTabStripPlaceholderView*)generateTabStripPlaceholderView;
 
 // Holds a snapshot view of the browser view controller's toolbar.
 @property(nonatomic, retain) UIView* toolbarSnapshotView;
 
-// Index of the selected tab in the browser view controller when the transition
-// context content was created.
-@property(nonatomic, assign) NSInteger initialSelectedTabIndex;
+// The tabID that was in the browser view controller when the transition context
+// content was created. Used to understand what might have changed in the model
+// when entering and leaving the tab switcher.
+@property(nonatomic, copy) NSString* initialTabID;
 @end
 
 // A Tab switcher transition context holds the informations needed to compute
 // the transition from a browser view controller to the tab switcher view
 // controller.
 @interface TabSwitcherTransitionContext : NSObject
 
 // Create a tab switcher transition context from the current browser view
 // controller, the main view controller (regular) and the off the record view
 // controller (incognito).
@@ skipping 13 matching lines @@
 // record) browser view controller.
 @property(nonatomic, retain)
     TabSwitcherTransitionContextContent* regularContent;
 // The tab model of the broswser view controller selected when the transition
 // context was created.
 @property(nonatomic, retain) TabModel* initialTabModel;
 
 @end
 
 #endif  // IOS_CHROME_BROWSER_UI_TAB_SWITCHER_TAB_SWITCHER_TRANSITION_CONTEXT_H_