cc: Make OutputSurface::BindToClient pure virtual and not return bool

cc/test/pixel_test_output_surface.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_TEST_PIXEL_TEST_OUTPUT_SURFACE_H_
 #define CC_TEST_PIXEL_TEST_OUTPUT_SURFACE_H_
 
 #include "base/memory/weak_ptr.h"
 #include "cc/output/output_surface.h"
 
 namespace cc {
 
 class PixelTestOutputSurface : public OutputSurface {
  public:
   explicit PixelTestOutputSurface(
       scoped_refptr<ContextProvider> context_provider,
       bool flipped_output_surface);
   explicit PixelTestOutputSurface(
       std::unique_ptr<SoftwareOutputDevice> software_device);
   ~PixelTestOutputSurface() override;
 
   // OutputSurface implementation.
+  void BindToClient(OutputSurfaceClient* client) override;
   void EnsureBackbuffer() override;
   void DiscardBackbuffer() override;
   void BindFramebuffer() override;
   void Reshape(const gfx::Size& size,
                float device_scale_factor,
                const gfx::ColorSpace& color_space,
                bool has_alpha) override;
   bool HasExternalStencilTest() const override;
   void ApplyExternalStencil() override;
   void SwapBuffers(OutputSurfaceFrame frame) override;
   OverlayCandidateValidator* GetOverlayCandidateValidator() const override;
   bool IsDisplayedAsOverlayPlane() const override;
   unsigned GetOverlayTextureId() const override;
   bool SurfaceIsSuspendForRecycle() const override;
   uint32_t GetFramebufferCopyTextureFormat() override;
 
   void set_has_external_stencil_test(bool has_test) {
     external_stencil_test_ = has_test;
   }
 
  private:
   void SwapBuffersCallback();
 
   bool external_stencil_test_ = false;
+  OutputSurfaceClient* client_ = nullptr;
   base::WeakPtrFactory<PixelTestOutputSurface> weak_ptr_factory_;
 };
 
 }  // namespace cc
 
 #endif  // CC_TEST_PIXEL_TEST_OUTPUT_SURFACE_H_