Send vsync timebase updates to the browser compositor

gpu/ipc/command_buffer_proxy.h

Index: gpu/ipc/command_buffer_proxy.h
diff --git a/gpu/ipc/command_buffer_proxy.h b/gpu/ipc/command_buffer_proxy.h
index 156d28dd856ae18ffa6ff4c4f731aa536394f8f1..5f058b3abf21988ccd49c56300eab75ff74ac6e5 100644
--- a/gpu/ipc/command_buffer_proxy.h
+++ b/gpu/ipc/command_buffer_proxy.h
@@ -57,6 +57,10 @@ class GPU_EXPORT CommandBufferProxy : public gpu::CommandBuffer {
       const base::Callback<void(const GpuMemoryAllocationForRenderer&)>&
           callback) = 0;
 
+  // Register a callback to invoke whenever we receive an updated vsync time.
+  virtual void SetUpdateVSyncTimeCallback(
+    const base::Callback<void(int64)>& callback) = 0;
+
   // Reparent a command buffer. TODO(apatrick): going forward, the notion of
   // the parent / child relationship between command buffers is going away in
   // favor of the notion of surfaces that can be drawn to in one command buffer