Integrate InstanceID with GCM crypto provider

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 f87bc2a3d6ef9b26d5c9bac3704e71a9d7cbbf67..39c7961909fe4e499b301c535dfd0843defb22df 100644
--- a/components/gcm_driver/gcm_driver.h
+++ b/components/gcm_driver/gcm_driver.h
@@ -138,7 +138,8 @@ class GCMDriver {
 
   // Get the public encryption key and the authentication secret associated with
   // |app_id|. If none have been associated with |app_id| yet, they will be
-  // created. The |callback| will be invoked when it is available.
+  // created. The |callback| will be invoked when it is available. Only use with
+  // GCM registrations; use InstanceID::GetEncryptionInfo for InstanceID tokens.
   void GetEncryptionInfo(const std::string& app_id,
                          const GetEncryptionInfoCallback& callback);
 
@@ -237,6 +238,11 @@ class GCMDriver {
                                     int interval_ms) = 0;
   virtual void RemoveHeartbeatInterval(const std::string& scope) = 0;
 
+  // Should only be used by the InstanceID system.
+  GCMEncryptionProvider* encryption_provider_internal() {

[Peter Beverloo, 2016/05/11 16:04:59]

(1) Please move this after GetInstanceIDHandlerInternal() to group them
together.
(2) Please rename this to GetEncryptionProviderInternal() for consistency. As
such, also move to .cc.
(3) Have a brief half-sentence describing *what* it is.

[johnme, 2016/05/13 16:25:45]

Done.

+    return &encryption_provider_;
+  }
+
  protected:
   // Ensures that the GCM service starts (if necessary conditions are met).
   virtual GCMClient::Result EnsureStarted(GCMClient::StartMode start_mode) = 0;