Push API: register PushMessagingServiceImpl as GCMAppHandler.

components/gcm_driver/gcm_driver.h

Index: components/gcm_driver/gcm_driver.h
diff --git a/components/gcm_driver/gcm_driver.h b/components/gcm_driver/gcm_driver.h
index 40e18666881027ee0236277df2f914f333401664..69d7756c4c4769df1fcb97da5380dbeed661c2a6 100644
--- a/components/gcm_driver/gcm_driver.h
+++ b/components/gcm_driver/gcm_driver.h
@@ -81,6 +81,9 @@ class GCMDriver {
   // Remove the handler for a given app.
   virtual void RemoveAppHandler(const std::string& app_id);
 
+  // Returns the handler for the given app.
+  GCMAppHandler* GetAppHandler(const std::string& app_id);
+
   // Enables/disables GCM service.
   virtual void Enable() = 0;
   virtual void Disable() = 0;
@@ -141,9 +144,6 @@ class GCMDriver {
 
   void ClearCallbacks();
 
-  // Returns the handler for the given app.
-  GCMAppHandler* GetAppHandler(const std::string& app_id);
-
  private:
   // Should be called when an app with |app_id| is trying to un/register.
   // Checks whether another un/registration is in progress.