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

cc/test/pixel_test_output_surface.h

Index: cc/test/pixel_test_output_surface.h
diff --git a/cc/test/pixel_test_output_surface.h b/cc/test/pixel_test_output_surface.h
index 6f1bc35df42a548dda3e7432874a72321bdf100c..7192c69290a422c6b72d54f71fe187bf240bd7c5 100644
--- a/cc/test/pixel_test_output_surface.h
+++ b/cc/test/pixel_test_output_surface.h
@@ -20,6 +20,7 @@ class PixelTestOutputSurface : public OutputSurface {
   ~PixelTestOutputSurface() override;
 
   // OutputSurface implementation.
+  void BindToClient(OutputSurfaceClient* client) override;
   void EnsureBackbuffer() override;
   void DiscardBackbuffer() override;
   void BindFramebuffer() override;
@@ -44,6 +45,7 @@ class PixelTestOutputSurface : public OutputSurface {
   void SwapBuffersCallback();
 
   bool external_stencil_test_ = false;
+  OutputSurfaceClient* client_ = nullptr;
   base::WeakPtrFactory<PixelTestOutputSurface> weak_ptr_factory_;
 };