[zoom bubble] Add tests for ZoomController::UpdateState() handling empty hosts.

chrome/browser/ui/zoom/zoom_controller.h

Index: chrome/browser/ui/zoom/zoom_controller.h
diff --git a/chrome/browser/ui/zoom/zoom_controller.h b/chrome/browser/ui/zoom/zoom_controller.h
index f7aed95ba46d1245da291190d5523d918b8fa379..c9617956dfff9019681af85dab5cca4652409bb3 100644
--- a/chrome/browser/ui/zoom/zoom_controller.h
+++ b/chrome/browser/ui/zoom/zoom_controller.h
@@ -38,10 +38,6 @@ class ZoomController : public content::NotificationObserver,
 
   void set_observer(ZoomObserver* observer) { observer_ = observer; }
 
- private:
-  explicit ZoomController(content::WebContents* web_contents);
-  friend class content::WebContentsUserData<ZoomController>;
-
   // content::WebContentsObserver overrides:
   virtual void DidNavigateMainFrame(
       const content::LoadCommittedDetails& details,
@@ -56,6 +52,11 @@ class ZoomController : public content::NotificationObserver,
   virtual void OnPreferenceChanged(PrefServiceBase* service,
                                    const std::string& pref_name) OVERRIDE;
 
+ private:
+  explicit ZoomController(content::WebContents* web_contents);
+  friend class content::WebContentsUserData<ZoomController>;
+  friend class ZoomControllerTest;
+
   // Updates the zoom icon and zoom percentage based on current values and
   // notifies the observer if changes have occurred. |host| may be empty,
   // meaning the change should apply to ~all sites. If it is not empty, the