[GCM] Add basic collapse key support for upstream

google_apis/gcm/engine/gcm_store.h

 // Copyright 2014 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.
 
 #ifndef GOOGLE_APIS_GCM_ENGINE_GCM_STORE_H_
 #define GOOGLE_APIS_GCM_ENGINE_GCM_STORE_H_
 
 #include <map>
 #include <string>
 #include <vector>
@@ skipping 73 matching lines @@
   virtual void RemoveIncomingMessages(const PersistentIdList& persistent_ids,
                                       const UpdateCallback& callback) = 0;
 
   // Unacknowledged outgoing messages handling.
   // Returns false if app has surpassed message limits, else returns true. Note
   // that the message isn't persisted until |callback| is invoked with
   // |success| == true.
   virtual bool AddOutgoingMessage(const std::string& persistent_id,
                                   const MCSMessage& message,
                                   const UpdateCallback& callback) = 0;
+  virtual void OverwriteOutgoingMessage(const std::string& persistent_id,
+                                        const MCSMessage& message,
+                                        const UpdateCallback& callback) = 0;
   virtual void RemoveOutgoingMessage(const std::string& persistent_id,
                                      const UpdateCallback& callback) = 0;
   virtual void RemoveOutgoingMessages(const PersistentIdList& persistent_ids,
                                       const UpdateCallback& callback) = 0;
 
   // User serial number handling.
   virtual void SetNextSerialNumber(int64 next_serial_number,
                                    const UpdateCallback& callback) = 0;
   virtual void AddUserSerialNumber(const std::string& username,
                                    int64 serial_number,
                                    const UpdateCallback& callback) = 0;
   virtual void RemoveUserSerialNumber(const std::string& username,
                                       const UpdateCallback& callback) = 0;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(GCMStore);
 };
 
 }  // namespace gcm
 
 #endif  // GOOGLE_APIS_GCM_ENGINE_GCM_STORE_H_