Use correct snapshot for the tab transition animation on iPad

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

Index: ios/chrome/browser/ui/tab_switcher/tab_switcher_controller.mm
diff --git a/ios/chrome/browser/ui/tab_switcher/tab_switcher_controller.mm b/ios/chrome/browser/ui/tab_switcher/tab_switcher_controller.mm
index 12db3675405241372ef676ba85877956b4998773..6f341dc971f68a00f1c434bc3bed41d990d7503f 100644
--- a/ios/chrome/browser/ui/tab_switcher/tab_switcher_controller.mm
+++ b/ios/chrome/browser/ui/tab_switcher/tab_switcher_controller.mm
@@ -568,8 +568,11 @@ enum class SnapshotViewOption {
   base::WeakNSObject<UIImageView> weakTabScreenshotImageView(
       tabScreenshotImageView.get());
 
-  if (self.transitionContext.initialTabModel != tabModel ||
-      transitionContextContent.initialSelectedTabIndex != selectedTabIndex) {
+  if (![self initialTabModelAndTabIDMatchesTabModel:tabModel

[jif, 2017/03/30 19:50:58]

Can you write the code without the "!" (i.e. swap the content of the
if...else... block)?

+                                              tabID:selectedTab.tabId]) {
+    // If transitioning to a different tab than the one animated in
+    // from, a new snapshot should be generated instead of using the transition
+    // context...

[jif, 2017/03/30 19:50:58]

no need for the "..."

     tabScreenshotImageView.get().image =
         [self updateScreenshotForCellIfNeeded:selectedCell tabModel:tabModel];
     [selectedTab retrieveSnapshot:^(UIImage* snapshot) {
@@ -716,6 +719,14 @@ enum class SnapshotViewOption {
                    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]];