Introduce CryptAuthGCMManager, which handles GCM interactions for CryptAuth.

components/proximity_auth/cryptauth/pref_names.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/proximity_auth/cryptauth/pref_names.h"
 
 namespace proximity_auth {
 namespace prefs {
 
 // Whether the system is scheduling device_syncs more aggressively to recover
@@ skipping 23 matching lines @@
 
 // The timestamp of the last successfull CryptAuth enrollment in seconds.
 const char kCryptAuthEnrollmentLastEnrollmentTimeSeconds[] =
     "cryptauth.enrollment.last_enrollment_time_seconds";
 
 // The reason that the next enrollment is performed. This should be one of the
 // enum values of InvocationReason in
 // components/proximity_auth/cryptauth/proto/cryptauth_api.proto.
 extern const char kCryptAuthEnrollmentReason[] = "cryptauth.enrollment.reason";
 
+// The GCM registration id used for receiving push messages from CryptAuth.
+extern const char kCryptAuthGCMRegistrationId[] =
+    "cryptauth.gcm_registration_id";
+
 }  // namespace prefs
 }  // proximity_auth