[Mac]Implement ViewID support.

chrome/browser/cocoa/tab_strip_controller.mm

Index: chrome/browser/cocoa/tab_strip_controller.mm
diff --git a/chrome/browser/cocoa/tab_strip_controller.mm b/chrome/browser/cocoa/tab_strip_controller.mm
index d2caf62652bfaa99ad8efae27f1be51ebad0ae0a..68bd984fbc734670b066abb77c9fdf17d2463b17 100644
--- a/chrome/browser/cocoa/tab_strip_controller.mm
+++ b/chrome/browser/cocoa/tab_strip_controller.mm
@@ -653,6 +653,22 @@ private:
   return tabStripModel_->IsContextMenuCommandEnabled(index, command) ? YES : NO;
 }
 
+// Returns the index of the tab controller. Returns -1 if not present.
+// Unlike modelIndexForTabView, this method does not care about whether the tab
+// is closing or not.
+- (NSInteger)indexForTabController:(TabController*)controller
+                           inTotal:(NSInteger*)total {
+  if (total)
+    *total = [tabArray_ count];
+  NSInteger index = 0;
+  for (TabController* current in tabArray_.get()) {
+    if (current  == controller)
+      return index;
+    ++index;
+  }
+  return -1;
+}
+
 - (void)insertPlaceholderForTab:(TabView*)tab
                           frame:(NSRect)frame
                   yStretchiness:(CGFloat)yStretchiness {