gpu: Add sync token dependencies to flush metadata.

gpu/command_buffer/client/gpu_control.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 GPU_COMMAND_BUFFER_CLIENT_GPU_CONTROL_H_
 #define GPU_COMMAND_BUFFER_CLIENT_GPU_CONTROL_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 80 matching lines @@
 
   // Returns true if the service has received the fence sync. Used for verifying
   // sync tokens.
   virtual bool IsFenceSyncFlushReceived(uint64_t release) = 0;
 
   // Returns true if the service has released (executed) the fence sync. Some
   // implementations may support calling this from any thread without holding
   // the lock provided by the client.
   virtual bool IsFenceSyncReleased(uint64_t release) = 0;
 
-  // Runs |callback| when sync token is signalled.
+  // Runs |callback| when sync token is signaled.
   virtual void SignalSyncToken(const SyncToken& sync_token,
                                const base::Closure& callback) = 0;
 
+  // Returns true if the wait is valid. This is used in addition to

[piman, 2017/03/13 23:17:39]

nit: it doesn't return anything.

[sunnyps, 2017/03/15 00:03:08]

Done.

+  // WaitSyncToken in the command buffer. The wait command is used to pull
+  // texture updates from other threads when used with MailboxManagerSync.

[piman, 2017/03/13 23:17:39]

I don't think this one has anything to do with pulling texture updates - it's
about giving a hint that the next Flush will wait on this...

[sunnyps, 2017/03/15 00:03:08]

The comment was about why the WaitSyncToken command in the command buffer is
necessary. I've rewritten this and hopefully it's clear now.

+  virtual void WaitSyncToken(const SyncToken& sync_token) = 0;
+
   // Under some circumstances a sync token may be used which has not been
-  // verified to have been flushed. For example, fence syncs queued on the
-  // same channel as the wait command guarantee that the fence sync will
-  // be enqueued first so does not need to be flushed.
-  virtual bool CanWaitUnverifiedSyncToken(const SyncToken* sync_token) = 0;
+  // verified to have been flushed. For example, fence syncs queued on the same
+  // channel as the wait command guarantee that the fence sync will be enqueued
+  // first so does not need to be flushed.
+  virtual bool CanWaitUnverifiedSyncToken(const SyncToken& sync_token) = 0;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(GpuControl);
 };
 
 }  // namespace gpu
 
 #endif  // GPU_COMMAND_BUFFER_CLIENT_GPU_CONTROL_H_