[Mac]Implement ViewID support. (third approach)

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..1a907bd65519fe8edafa7cc676ff901ecb3dde9f 100644
--- a/chrome/browser/cocoa/tab_strip_controller.mm
+++ b/chrome/browser/cocoa/tab_strip_controller.mm
@@ -581,6 +581,10 @@ private:
   return [[tabArray_ objectAtIndex:index] view];
 }
 
+- (NSUInteger)viewsCount {
+  return [tabArray_ count];
+}
+
 // Called when the user clicks a tab. Tell the model the selection has changed,
 // which feeds back into us via a notification.
 - (void)selectTab:(id)sender {