Add fence support for TransferBuffers

src/gpu/gl/GrGLGpu.h

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrGLGpu_DEFINED
 #define GrGLGpu_DEFINED
 
@@ skipping 126 matching lines @@
                                                     bool isRenderTarget = false) override;
     bool isTestingOnlyBackendTexture(GrBackendObject) const override;
     void deleteTestingOnlyBackendTexture(GrBackendObject, bool abandonTexture) override;
 
     void resetShaderCacheForTesting() const override;
 
     void drawDebugWireRect(GrRenderTarget*, const SkIRect&, GrColor) override;
 
     void finishDrawTarget() override;
 
+    GrFence SK_WARN_UNUSED_RESULT insertFence() const override;
+    bool waitFence(GrFence, uint64_t timeout) const override;
+    void deleteFence(GrFence) const override;
+
 private:
     GrGLGpu(GrGLContext* ctx, GrContext* context);
 
     // GrGpu overrides
     void onResetContext(uint32_t resetBits) override;
 
     void xferBarrier(GrRenderTarget*, GrXferBarrierType) override;
 
     GrTexture* onCreateTexture(const GrSurfaceDesc& desc, SkBudgeted budgeted,
                                const SkTArray<GrMipLevel>& texels) override;
@@ skipping 481 matching lines @@
     bool fPLSHasBeenUsed;
 
     float fHWMinSampleShading;
 
     typedef GrGpu INHERITED;
     friend class GrGLPathRendering; // For accessing setTextureUnit.
     friend class gr_instanced::GLInstancedRendering; // For accessing flushGLState.
 };
 
 #endif