[ios] Use WebStateList to back the tab grid.

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

Index: ios/clean/chrome/browser/ui/tab_grid/tab_grid_view_controller.mm
diff --git a/ios/clean/chrome/browser/ui/tab_grid/tab_grid_view_controller.mm b/ios/clean/chrome/browser/ui/tab_grid/tab_grid_view_controller.mm
index 9ee9700b5b41eb6a12677446277f2dbadc36421c..2ae53750627fb37dd0a2c75e3e3d7693e2eb8294 100644
--- a/ios/clean/chrome/browser/ui/tab_grid/tab_grid_view_controller.mm
+++ b/ios/clean/chrome/browser/ui/tab_grid/tab_grid_view_controller.mm
@@ -105,7 +105,9 @@ const CGFloat kToolbarHeight = 64.0f;
 
 - (NSInteger)collectionView:(UICollectionView*)collectionView
      numberOfItemsInSection:(NSInteger)section {
-  NSInteger items = [self.dataSource numberOfTabsInTabGrid];
+  int tabs = [self.dataSource numberOfTabsInTabGrid];
+  DCHECK_LE(tabs, NSIntegerMax);

[sdefresne, 2017/03/14 09:04:08]

This is unnecessary, NSInteger is at least as large as int.

From Objective-C documentation:
  > When building 32-bit applications, NSInteger is a 32-bit integer.
  > A 64-bit application treats NSInteger as a 64-bit integer.

NSInteger is in fact a typedef for long, and the C (and C++) standard guarantees
that long is at least as large as int (in fact, it order types in char, short,
int, long, long long and guarantees that each is at least as large as the
previous one and only gives lower bound on the type size).

TL;DR: remove the DCHECK and cast here.

[edchin, 2017/03/14 16:02:42]

Done.

+  NSInteger items = static_cast<NSInteger>(tabs);
   // HACK: Do not make showing noTabsOverlay a side effect of the dataSource
   // callback.
   if (items) {
@@ -124,10 +126,15 @@ const CGFloat kToolbarHeight = 64.0f;
                                     forIndexPath:indexPath]);
   cell.delegate = self;
   [cell setSessionType:TabSwitcherSessionType::REGULAR_SESSION];
-  [cell setAppearanceForTabTitle:[self.dataSource titleAtIndex:indexPath.item]
+  DCHECK_LE(indexPath.item, INT_MAX);
+  int item = static_cast<int>(indexPath.item);
+  [cell setAppearanceForTabTitle:[self.dataSource titleAtIndex:item]
                          favicon:nil
                         cellSize:CGSizeZero];
-  [cell setSelected:(indexPath.item == [self.dataSource indexOfActiveTab])];
+  int tab = [self.dataSource indexOfActiveTab];
+  DCHECK_LE(tab, NSIntegerMax);

[sdefresne, 2017/03/14 09:04:08]

ditto, remove the DCHECK and cast here (int -> NSInteger is safe)

+  NSInteger index = static_cast<NSInteger>(tab);
+  [cell setSelected:(indexPath.item == index)];
   return cell;
 }
 
@@ -162,13 +169,13 @@ const CGFloat kToolbarHeight = 64.0f;
 }
 
 - (void)createNewTab:(id)sender {
-  // PLACEHOLDER: The new WebStateList data structure will have implications
-  // on how new tabs are created.
   NSInteger index = [self.grid numberOfItemsInSection:0];
   NSIndexPath* indexPath = [NSIndexPath indexPathForItem:index inSection:0];
   auto updateBlock = ^{
     // Unselect current selected item.
-    NSInteger selectedIndex = [self.dataSource indexOfActiveTab];
+    int index = [self.dataSource indexOfActiveTab];
+    DCHECK_LE(index, NSIntegerMax);

[sdefresne, 2017/03/14 09:04:08]

ditto, remove the DCHECK and cast here (int -> NSInteger is safe)

+    NSInteger selectedIndex = static_cast<NSInteger>(index);
     NSIndexPath* selectedIndexPath =
         [NSIndexPath indexPathForItem:selectedIndex inSection:0];
     [self.grid reloadItemsAtIndexPaths:@[ selectedIndexPath ]];
@@ -189,7 +196,9 @@ const CGFloat kToolbarHeight = 64.0f;
 }
 
 - (void)cellPressed:(UICollectionViewCell*)cell {
-  NSInteger selectedIndex = [self.dataSource indexOfActiveTab];
+  int index = [self.dataSource indexOfActiveTab];
+  DCHECK_LE(index, NSIntegerMax);

[sdefresne, 2017/03/14 09:04:09]

ditto, remove the DCHECK and cast here (int -> NSInteger is safe)

+  NSInteger selectedIndex = static_cast<NSInteger>(index);
   NSIndexPath* newSelectedIndexPath = [self.grid indexPathForCell:cell];
   [self.tabCommandHandler showTabAtIndexPath:newSelectedIndexPath];
   if (newSelectedIndexPath.item != selectedIndex) {