gpu: Allow waiting on sync tokens without sync token client.

gpu/command_buffer/service/gles2_cmd_decoder.h

Index: gpu/command_buffer/service/gles2_cmd_decoder.h
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.h b/gpu/command_buffer/service/gles2_cmd_decoder.h
index c53b5224c6b935b198d37cd56af4311096714f29..d7d8a232d4a5c4f827caf90eb05de46cc0ddac9c 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.h
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.h
@@ -36,6 +36,7 @@ class Size;
 namespace gpu {
 
 struct Mailbox;
+struct SyncToken;
 
 namespace gles2 {
 
@@ -85,10 +86,7 @@ class GPU_EXPORT GLES2Decoder : public base::SupportsWeakPtr<GLES2Decoder>,
  public:
   typedef error::Error Error;
   typedef base::Callback<void(uint64_t release)> FenceSyncReleaseCallback;
-  typedef base::Callback<bool(gpu::CommandBufferNamespace namespace_id,
-                              gpu::CommandBufferId command_buffer_id,
-                              uint64_t release)>
-      WaitFenceSyncCallback;
+  typedef base::Callback<bool(const gpu::SyncToken&)> WaitSyncTokenCallback;
   typedef base::Callback<void(void)> NoParamCallback;
 
   // The default stencil mask, which has all bits set.  This really should be a
@@ -281,11 +279,12 @@ class GPU_EXPORT GLES2Decoder : public base::SupportsWeakPtr<GLES2Decoder>,
   virtual void SetShaderCacheCallback(const ShaderCacheCallback& callback) = 0;
 
   // Sets the callback for fence sync release and wait calls. The wait call
-  // returns true if the channel is still scheduled.
+  // returns false if the wait was a nop or invalid and the command buffer is
+  // still scheduled.
   virtual void SetFenceSyncReleaseCallback(
       const FenceSyncReleaseCallback& callback) = 0;
-  virtual void SetWaitFenceSyncCallback(
-      const WaitFenceSyncCallback& callback) = 0;
+  virtual void SetWaitSyncTokenCallback(
+      const WaitSyncTokenCallback& callback) = 0;
 
   // Sets the callback for the DescheduleUntilFinished and
   // RescheduleAfterFinished calls.