Switch ZoomTabHelper to use WebContentsUserData.

chrome/browser/ui/zoom/zoom_observer.h

Index: chrome/browser/ui/zoom/zoom_observer.h
diff --git a/chrome/browser/ui/zoom/zoom_observer.h b/chrome/browser/ui/zoom/zoom_observer.h
index b16c7d7be5c0291bec6b8190d7ede18aa926b985..54f52e186b525c9964f0ea51f7b9cfbd98e94db1 100644
--- a/chrome/browser/ui/zoom/zoom_observer.h
+++ b/chrome/browser/ui/zoom/zoom_observer.h
@@ -5,13 +5,16 @@
 #ifndef CHROME_BROWSER_UI_ZOOM_ZOOM_OBSERVER_H_
 #define CHROME_BROWSER_UI_ZOOM_ZOOM_OBSERVER_H_
 
-class TabContents;
+namespace content {
+class WebContents;
+}
 
 // Interface for objects that wish to be notified of changes in ZoomController.
 class ZoomObserver {
  public:
   // Notification that the zoom percentage has changed.
-  virtual void OnZoomChanged(TabContents* source, bool can_show_bubble) = 0;
+  virtual void OnZoomChanged(content::WebContents* source,
+                             bool can_show_bubble) = 0;
 
  protected:
   virtual ~ZoomObserver() {}