Notify GCMAppHandlers when the store is reset, so they clear cached IDs

components/gcm_driver/gcm_app_handler.h

Index: components/gcm_driver/gcm_app_handler.h
diff --git a/components/gcm_driver/gcm_app_handler.h b/components/gcm_driver/gcm_app_handler.h
index 4ee8b906167f68bdf3bf52c44fcda9ba38b7c83b..934819c25c42b69b43e8ae965f4070b8ad221086 100644
--- a/components/gcm_driver/gcm_app_handler.h
+++ b/components/gcm_driver/gcm_app_handler.h
@@ -23,6 +23,15 @@ class GCMAppHandler {
   // make safe for ShutdownHandler to be called multiple times.
   virtual void ShutdownHandler() = 0;
 
+  // Called when the GCM store is reset (e.g. due to corruption), which changes
+  // the device ID, invalidating all prior registrations. Any stored state
+  // related to GCM registrations or InstanceIDs should be deleted. This should
+  // only be considered a defense in depth, as this method will not be called if
+  // the store is reset before this app handler is registered; hence it is
+  // recommended to regularly revalidate any stored registrations/InstanceIDs.
+  // TODO(johnme): GCMDriver doesn't yet provide an API for revalidating them.
+  virtual void OnStoreReset() = 0;
+
   // Called when a GCM message has been received.
   virtual void OnMessage(const std::string& app_id,
                          const IncomingMessage& message) = 0;