Implement future sync points in gpu service

mojo/services/public/interfaces/gpu/command_buffer.mojom

 // 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.
 
 module mojo;
 
 import "mojo/services/public/interfaces/gpu/gpu_capabilities.mojom";
 
 struct CommandBufferState {
   int32 num_entries;
@@ skipping 18 matching lines @@
 interface CommandBuffer {
   Initialize(CommandBufferSyncClient? sync_client,
              CommandBufferSyncPointClient? sync_point_client,
              handle<shared_buffer>? shared_state);
   SetGetBuffer(int32 buffer);
   Flush(int32 put_offset);
   MakeProgress(int32 last_get_offset);
   RegisterTransferBuffer(
       int32 id, handle<shared_buffer>? transfer_buffer, uint32 size);
   DestroyTransferBuffer(int32 id);
-  InsertSyncPoint();  // Sync point returned via DidInsertSyncPoint
+
+  // InsertSyncPoint returns the sync point returned via DidInsertSyncPoint.
+  // If |retire| is true, the sync point is retired on insertion. Otherwise,
+  // explicitly call RetireSyncPoint to retire it.
+  InsertSyncPoint(bool retire);
+  RetireSyncPoint(uint32 sync_point);
   Echo() => ();
 
   // TODO(piman): sync points
 };
 
 interface CommandBufferClient {
   DidDestroy();
   LostContext(int32 lost_reason);  // TODO(piman): enum
 };