cc: Make OutputSurface::SwapBuffers pure virtual

cc/output/renderer_unittest.cc

Index: cc/output/renderer_unittest.cc
diff --git a/cc/output/renderer_unittest.cc b/cc/output/renderer_unittest.cc
index 99ff89d569388346406ee7bbc4276bbc6db9975c..23719edc0fd4dd78355ab50807ddf0f0e53cba58 100644
--- a/cc/output/renderer_unittest.cc
+++ b/cc/output/renderer_unittest.cc
@@ -15,6 +15,29 @@
 namespace cc {
 namespace {
 
+class TestOutputSurface : public OutputSurface {
+ public:
+  explicit TestOutputSurface(
+      const scoped_refptr<ContextProvider>& context_provider);
+  virtual ~TestOutputSurface() override;
+
+  // OutputSurface implementation
+  virtual void SwapBuffers(CompositorFrame* frame) override;
+};
+
+TestOutputSurface::TestOutputSurface(
+    const scoped_refptr<ContextProvider>& context_provider)
+    : OutputSurface(context_provider) {
+}
+
+TestOutputSurface::~TestOutputSurface() {
+}
+
+void TestOutputSurface::SwapBuffers(CompositorFrame* frame) {
+  client_->DidSwapBuffers();
+  client_->DidSwapBuffersComplete();
+}
+
 class MockContextProvider : public TestContextProvider {
  public:
   explicit MockContextProvider(scoped_ptr<TestWebGraphicsContext3D> context)
@@ -57,7 +80,7 @@ class RendererTest : public ::testing::Test {
   virtual void SetUp() {
     context_provider_ =
         new MockContextProvider(TestWebGraphicsContext3D::Create());
-    output_surface_.reset(new OutputSurface(context_provider_));
+    output_surface_.reset(new TestOutputSurface(context_provider_));
     output_surface_->BindToClient(&output_surface_client_);
     resource_provider_ = ResourceProvider::Create(
         output_surface_.get(), NULL, NULL, 0, false, 1, false);