gpu: Add GpuFence framework.

gpu/command_buffer/client/gpu_control.h

Index: gpu/command_buffer/client/gpu_control.h
diff --git a/gpu/command_buffer/client/gpu_control.h b/gpu/command_buffer/client/gpu_control.h
index 813d5630960734f3f1c3661bed5048cc9ab70f01..5398a8fbd1709f8e38c85d830d01886c9395a9c9 100644
--- a/gpu/command_buffer/client/gpu_control.h
+++ b/gpu/command_buffer/client/gpu_control.h
@@ -19,6 +19,7 @@
 #include "gpu/gpu_export.h"
 
 extern "C" typedef struct _ClientBuffer* ClientBuffer;
+extern "C" typedef struct _ClientFence* ClientFence;
 
 namespace base {
 class Lock;
@@ -108,6 +109,12 @@ class GPU_EXPORT GpuControl {
   // be enqueued first so does not need to be flushed.
   virtual bool CanWaitUnverifiedSyncToken(const SyncToken* sync_token) = 0;
 
+  // Create a fence for a client fence. Returns its ID or -1 on error.
+  virtual int32_t CreateFence(ClientFence fence) = 0;
+
+  // Destroy a fence. The ID must be positive.
+  virtual void DestroyFence(int32_t id) = 0;
+
  private:
   DISALLOW_COPY_AND_ASSIGN(GpuControl);
 };