[Mac]Implement ViewID support.

chrome/browser/cocoa/tab_view.mm

Index: chrome/browser/cocoa/tab_view.mm
diff --git a/chrome/browser/cocoa/tab_view.mm b/chrome/browser/cocoa/tab_view.mm
index 7f34aa582d240278b37fa814fafe415b04dbaa00..7fa718623fb105916e6f3281aab698a5d16d3243 100644
--- a/chrome/browser/cocoa/tab_view.mm
+++ b/chrome/browser/cocoa/tab_view.mm
@@ -10,6 +10,7 @@
 #import "chrome/browser/cocoa/tab_controller.h"
 #import "chrome/browser/cocoa/tab_window_controller.h"
 #import "chrome/browser/cocoa/themed_window.h"
+#import "chrome/browser/cocoa/view_id_util.h"
 #include "grit/theme_resources.h"
 
 namespace {
@@ -864,6 +865,11 @@ const CGFloat kRapidCloseDist = 2.5;
   return [super accessibilityAttributeValue:attribute];
 }
 
+// Tag is used solely for ViewID. Override to prevent changing of it.
+- (NSInteger)tag {
+  return view_id_util::ViewIDToTag([controller_ viewID]);
+}
+
 @end  // @implementation TabView
 
 @implementation TabView (TabControllerInterface)