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

cc/test/fake_output_surface.cc

 // Copyright 2012 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.
 
 #include "cc/test/fake_output_surface.h"
 
 #include "base/bind.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "cc/output/output_surface_client.h"
 #include "cc/resources/returned_resource.h"
@@ skipping 54 matching lines @@
   context_provider_->ContextGL()->BindFramebuffer(GL_FRAMEBUFFER, framebuffer_);
 }
 
 uint32_t FakeOutputSurface::GetFramebufferCopyTextureFormat() {
   if (framebuffer_)
     return framebuffer_format_;
   else
     return GL_RGB;
 }
 
-bool FakeOutputSurface::BindToClient(OutputSurfaceClient* client) {
-  if (OutputSurface::BindToClient(client)) {
-    client_ = client;
-    return true;
-  } else {
-    return false;
-  }
+void FakeOutputSurface::BindToClient(OutputSurfaceClient* client) {
+  DCHECK(client);
+  DCHECK(!client_);
+  client_ = client;
 }
 
 bool FakeOutputSurface::HasExternalStencilTest() const {
   return has_external_stencil_test_;
 }
 
 bool FakeOutputSurface::SurfaceIsSuspendForRecycle() const {
   return suspended_for_recycle_;
 }
 
 OverlayCandidateValidator* FakeOutputSurface::GetOverlayCandidateValidator()
     const {
   return overlay_candidate_validator_;
 }
 
 bool FakeOutputSurface::IsDisplayedAsOverlayPlane() const {
   return false;
 }
 
 unsigned FakeOutputSurface::GetOverlayTextureId() const {
   return 0;
 }
 
 }  // namespace cc