gpu: Add GpuFence framework.

services/ui/ws/mus_gpu_memory_buffer_manager.h

Index: services/ui/ws/mus_gpu_memory_buffer_manager.h
diff --git a/services/ui/ws/mus_gpu_memory_buffer_manager.h b/services/ui/ws/mus_gpu_memory_buffer_manager.h
index a40a7438d1335deb2e84ae31e4629dc0f4df1b12..5afaa00526add4eba2c3f190ebc81c476519fb40 100644
--- a/services/ui/ws/mus_gpu_memory_buffer_manager.h
+++ b/services/ui/ws/mus_gpu_memory_buffer_manager.h
@@ -39,6 +39,10 @@ class MusGpuMemoryBufferManager : public gpu::GpuMemoryBufferManager {
       gfx::BufferFormat format) override;
   void SetDestructionSyncToken(gfx::GpuMemoryBuffer* buffer,
                                const gpu::SyncToken& sync_token) override;
+  std::unique_ptr<gfx::GpuFence> CreateGpuFence() override;
+  std::unique_ptr<gfx::GpuFence> CreateGpuFenceFromHandle(
+      const gfx::GpuFenceHandle& handle) override;
+  gfx::GpuFence* GpuFenceFromClientFence(ClientFence fence) override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(MusGpuMemoryBufferManager);