[iOS] Don't show selection change when leaving tab grid.

Per the attached bug, this CL changes the tab grid to not show the changed selection state when leaving the tab grid via a tap on a cell.

Cell selection actually happened twice when a cell was tapped; once directly from the collection view, and a second time after the selection had round-tripped through the mediator. This CL cleans that up, and has the collection view decline all selection events, allowing them only to happen as a result of consumer calls.

This CL adds a |showSelectionState| property to the grid view controller; when set to NO, the grid view controller will not update the selection state of the cells when the -selectWithItemID: consumer call is received. The ID of the selected item is maintained, however.

This Cl also doesn't show the selection ring on the proxy cells animated for the transition.

Bug: 849642

Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: Ibf8d2c91dc80c42dea55c7e457efe7232d234267
Reviewed-on: https://chromium-review.googlesource.com/1096763Reviewed-by: edchin <edchin@chromium.org>
Commit-Queue: Mark Cogan <marq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567192}

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

@@ -52,6 +52,9 @@
 // YES if the selected cell is visible in the grid.
 @property(nonatomic, readonly, getter=isSelectedCellVisible)
     BOOL selectedCellVisible;
+// YES if the gid should show cell selection updates. This would be set to NO,
+// for example, if the grid was about to be transitioned out of.
+@property(nonatomic, assign) BOOL showsSelectionUpdates;
 
 // Returns the layout of the grid for use in an animated transition.
 - (GridTransitionLayout*)transitionLayout;

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

@@ -63,6 +63,7 @@ NSIndexPath* CreateIndexPath(NSInteger index) {
 @synthesize delegate = _delegate;
 @synthesize imageDataSource = _imageDataSource;
 @synthesize emptyStateView = _emptyStateView;
+@synthesize showsSelectionUpdates = _showsSelectionUpdates;
 // Private properties.
 @synthesize viewAppeared = _viewAppeared;
 @synthesize collectionView = _collectionView;
@@ -75,6 +76,7 @@ NSIndexPath* CreateIndexPath(NSInteger index) {
 - (instancetype)init {
   if (self = [super init]) {
     _items = [[NSMutableArray<GridItem*> alloc] init];
+    _showsSelectionUpdates = YES;
   }
   return self;
 }
@@ -185,7 +187,7 @@ NSIndexPath* CreateIndexPath(NSInteger index) {
         [GridTransitionLayoutItem itemWithCell:[cell proxyForTransitions]
                                     attributes:attributes];
     [items addObject:item];
-    if (cell.selected) {
+    if ([cell.itemIdentifier isEqualToString:self.selectedItemID]) {
       selectedItem = item;
     }
   }
@@ -236,12 +238,16 @@ NSIndexPath* CreateIndexPath(NSInteger index) {
 
 #pragma mark - UICollectionViewDelegate
 
-- (void)collectionView:(UICollectionView*)collectionView
-    didSelectItemAtIndexPath:(NSIndexPath*)indexPath {
+// This method is used instead of -willSelectItemAtIndexPath, because any
+// selection events will be signalled through the model layer and handled in
+// the GridConsumer -selectItemWithID: method.
+- (BOOL)collectionView:(UICollectionView*)collectionView
+    shouldSelectItemAtIndexPath:(NSIndexPath*)indexPath {
   NSUInteger index = base::checked_cast<NSUInteger>(indexPath.item);
   DCHECK_LT(index, self.items.count);
   NSString* itemID = self.items[index].identifier;
   [self.delegate gridViewController:self didSelectItemWithID:itemID];
+  return NO;
 }
 
 #pragma mark - GridCellDelegate
@@ -337,7 +343,7 @@ NSIndexPath* CreateIndexPath(NSInteger index) {
 
 - (void)selectItemWithID:(NSString*)selectedItemID {
   self.selectedItemID = selectedItemID;
-  if (![self isViewAppeared])
+  if (!([self isViewAppeared] && self.showsSelectionUpdates))
     return;
   [self.collectionView
       selectItemAtIndexPath:CreateIndexPath(self.selectedIndex)

ios/chrome/browser/ui/tab_grid/tab_grid_view_controller.mm

@@ -755,6 +755,10 @@ NSUInteger GetPageIndexFromPage(TabGridPage page) {
 
 - (void)gridViewController:(GridViewController*)gridViewController
        didSelectItemWithID:(NSString*)itemID {
+  // Update the model with the tab selection, but don't have the grid view
+  // controller display the new selection, since there will be a transition
+  // away from it immediately afterwards.
+  gridViewController.showsSelectionUpdates = NO;
   if (gridViewController == self.regularTabsViewController) {
     [self.regularTabsDelegate selectItemWithID:itemID];
   } else if (gridViewController == self.incognitoTabsViewController) {
@@ -762,6 +766,7 @@ NSUInteger GetPageIndexFromPage(TabGridPage page) {
   }
   self.activePage = self.currentPage;
   [self.tabPresentationDelegate showActiveTabInPage:self.currentPage];
+  gridViewController.showsSelectionUpdates = YES;
 }
 
 - (void)gridViewController:(GridViewController*)gridViewController

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

@@ -70,7 +70,6 @@
       break;
     case GridAnimationDirectionExpanding:
       [self positionSelectedItemInRegularGrid];
-      self.layout.selectedItem.cell.selected = YES;
       [self positionUnselectedItemsInRegularGrid];
       break;
   }