Keep the GCM data intact when the user signs out of the profile

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 34391acaf7a514976811cdbd54fad776963b9455..87345178662a479528e9e764bd3c647f7ce838a9 100644
--- a/components/gcm_driver/gcm_driver.h
+++ b/components/gcm_driver/gcm_driver.h
@@ -72,9 +72,9 @@ class GCMDriver {
   // been called, no other GCMDriver methods may be used.
   virtual void Shutdown();
 
-  // Call this method when the user signs in to a GAIA account.
-  // TODO(jianli): To be removed when sign-in enforcement is dropped.
+  // Called when the user signs in to or out of a GAIA account.
   virtual void OnSignedIn() = 0;
+  virtual void OnSignedOut() = 0;
 
   // Removes all the cached and persisted GCM data. If the GCM service is
   // restarted after the purge, a new Android ID will be obtained.