[iOS] Use NTP snapshot in new tab animation from grid.

New tabs opened from the grid were shown as white as they animated open,
because they were only showing the cell's snapshot, not the snapshot
taken from the BVC that will be displayed.

This was because the gird animation only shows the BVC snapshot if it
thinks there will be a difference between it and the cell snapshot --
specifically when there's been a device rotation.

This CL lets the grid view controller flag the active cell in the
animation as "appearing" so that the animation can always show the
BVC's snapshot in that case.

Bug: 865978
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: Iede4af004e89e5fda1395c4257c3d74fd2a682c7
Reviewed-on: https://chromium-review.googlesource.com/1156685
Commit-Queue: Mark Cogan <marq@chromium.org>
Reviewed-by: edchin <edchin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579470}

ios/chrome/browser/ui/tab_grid/grid/grid_view_controller.mm

@@ -50,6 +50,9 @@ NSIndexPath* CreateIndexPath(NSInteger index) {
 @property(nonatomic, copy) NSString* selectedItemID;
 // Index of the selected item in |items|.
 @property(nonatomic, readonly) NSUInteger selectedIndex;
+// ID of the last item to be inserted. This is used to track if the active tab
+// was newly created when building the animation layout for transitions.
+@property(nonatomic, copy) NSString* lastInsertedItemID;
 // The gesture recognizer used for interactive item reordering.
 @property(nonatomic, strong)
     UILongPressGestureRecognizer* itemReorderRecognizer;
@@ -79,6 +82,7 @@ NSIndexPath* CreateIndexPath(NSInteger index) {
 @synthesize collectionView = _collectionView;
 @synthesize items = _items;
 @synthesize selectedItemID = _selectedItemID;
+@synthesize lastInsertedItemID = _lastInsertedItemID;
 @synthesize itemReorderRecognizer = _itemReorderRecognizer;
 @synthesize itemReorderTouchPoint = _itemReorderTouchPoint;
 @synthesize emptyStateAnimator = _emptyStateAnimator;
@@ -150,6 +154,7 @@ NSIndexPath* CreateIndexPath(NSInteger index) {
   // Update the delegate, in case it wasn't set when |items| was populated.
   [self.delegate gridViewController:self didChangeItemCount:self.items.count];
   [self animateEmptyStateOut];
+  self.lastInsertedItemID = nil;
 }
 
 - (void)viewWillDisappear:(BOOL)animated {
@@ -218,6 +223,10 @@ NSIndexPath* CreateIndexPath(NSInteger index) {
       activeItem = [GridTransitionActiveItem itemWithCell:activeCell
                                                    center:attributes.center
                                                      size:attributes.size];
+      // If the active item is the last inserted item, it needs to be animated
+      // differently.
+      if ([cell.itemIdentifier isEqualToString:self.lastInsertedItemID])
+        activeItem.isAppearing = YES;
       selectionItem = [GridTransitionItem
           itemWithCell:[GridTransitionSelectionCell transitionCellFromCell:cell]
                 center:attributes.center];
@@ -357,6 +366,7 @@ NSIndexPath* CreateIndexPath(NSInteger index) {
   auto modelUpdates = ^{
     [self.items insertObject:item atIndex:index];
     self.selectedItemID = selectedItemID;
+    self.lastInsertedItemID = item.identifier;
     [self.delegate gridViewController:self didChangeItemCount:self.items.count];
   };
   auto collectionViewUpdates = ^{

ios/chrome/browser/ui/tab_grid/transitions/grid_to_visible_tab_animator.mm

@@ -61,7 +61,6 @@
   [containerView addSubview:presentedView];
   presentedView.frame =
       [transitionContext finalFrameForViewController:presentedViewController];
-  presentedView.alpha = 0.0;
 
   // Get the layout of the grid for the transition.
   GridTransitionLayout* layout =
@@ -103,6 +102,10 @@
       [self.stateProvider proxyPositionForTransitionContext:transitionContext];
   [proxyContainer insertSubview:self.animation aboveSubview:viewBehindProxies];
 
+  // Make the presented view alpha-zero; this should happen after all snapshots
+  // are taken.
+  presentedView.alpha = 0.1;
+
   [self.animation.animator addCompletion:^(UIViewAnimatingPosition position) {
     BOOL finished = (position == UIViewAnimatingPositionEnd);
     [self gridTransitionAnimationDidFinish:finished];

ios/chrome/browser/ui/tab_grid/transitions/grid_transition_animation.mm

@@ -262,9 +262,13 @@ CGFloat DeviceCornerRadius() {
   // is shown.
 
   UIView<GridToTabTransitionView>* activeCell = self.layout.activeItem.cell;
-  // The top and main tab views start at zero alpha but are crossfaded in.
-  activeCell.mainTabView.alpha = 0.0;
+  // The top tab view starts at zero alpha but is crossfaded in.
   activeCell.topTabView.alpha = 0.0;
+  // If the active item is appearing, the main tab view is shown. If not, it's
+  // hidden, and may be faded in if it's expected to be different in content
+  // from the existing cell snapshot.
+  if (!self.layout.activeItem.isAppearing)
+    activeCell.mainTabView.alpha = 0.0;
 
   // A: Zoom the active cell into position.
   UIViewPropertyAnimator* zoomActiveCell =

ios/chrome/browser/ui/tab_grid/transitions/grid_transition_layout.h

@@ -75,6 +75,9 @@
 // The size of |cell| in the grid.
 @property(nonatomic, readonly) CGSize size;
 
+// YES if the item is "appearing" in the grid as part of this animation.
+@property(nonatomic, assign) BOOL isAppearing;
+
 // Creates a new active item instance with |cell|, |center| and |size|.
 + (instancetype)itemWithCell:(UIView<GridToTabTransitionView>*)cell
                       center:(CGPoint)center

ios/chrome/browser/ui/tab_grid/transitions/grid_transition_layout.mm

@@ -65,6 +65,7 @@
 @implementation GridTransitionActiveItem
 @dynamic cell;
 @synthesize size = _size;
+@synthesize isAppearing = _isAppearing;
 
 + (instancetype)itemWithCell:(UIView<GridToTabTransitionView>*)cell
                       center:(CGPoint)center