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

cc/trees/layer_tree_host_unittest_copyrequest.cc

Index: cc/trees/layer_tree_host_unittest_copyrequest.cc
diff --git a/cc/trees/layer_tree_host_unittest_copyrequest.cc b/cc/trees/layer_tree_host_unittest_copyrequest.cc
index c572dcbc830791ab0699e450394833d30df7278c..15ebf33f84b3928261dc917c06174511f9e10aa3 100644
--- a/cc/trees/layer_tree_host_unittest_copyrequest.cc
+++ b/cc/trees/layer_tree_host_unittest_copyrequest.cc
@@ -140,6 +140,7 @@ class LayerTreeHostCopyRequestTestMultipleRequests
         TestContextProvider::Create();
     TestContextSupport* context_support = display_context_provider->support();
     context_support->set_out_of_order_callbacks(out_of_order_callbacks_);
+    display_context_provider->BindToCurrentThread();
 
     return FakeOutputSurface::Create3d(std::move(display_context_provider));
   }
@@ -734,6 +735,7 @@ class LayerTreeHostCopyRequestTestDeleteTexture
   std::unique_ptr<OutputSurface> CreateDisplayOutputSurfaceOnThread(
       scoped_refptr<ContextProvider> compositor_context_provider) override {
     display_context_provider_ = TestContextProvider::Create();
+    display_context_provider_->BindToCurrentThread();
     return FakeOutputSurface::Create3d(display_context_provider_);
   }
 
@@ -789,6 +791,9 @@ class LayerTreeHostCopyRequestTestDeleteTexture
     // to be destroyed by the compositor, so we should have 1 less by now.
     EXPECT_EQ(num_textures_after_readback_ - 1,
               display_context_provider_->TestContext3d()->NumTextures());
+
+    // Unref the context provider on the compositor thread.
+    display_context_provider_ = nullptr;
     EndTest();
   }