cc: Make LayerTreeHostImpl unittests use a delegating output surface.

cc/test/test_context_provider.h

Index: cc/test/test_context_provider.h
diff --git a/cc/test/test_context_provider.h b/cc/test/test_context_provider.h
index f294eb7ecd5ba42c7dfbda03498eb3b42026f0dc..97c7abcd3b5bae42affb7ad1b768e9e2723f58fb 100644
--- a/cc/test/test_context_provider.h
+++ b/cc/test/test_context_provider.h
@@ -35,6 +35,8 @@ class TestContextProvider : public ContextProvider {
   static scoped_refptr<TestContextProvider> CreateWorker();
   static scoped_refptr<TestContextProvider> Create(
       std::unique_ptr<TestWebGraphicsContext3D> context);
+  static scoped_refptr<TestContextProvider> Create(
+      std::unique_ptr<TestGLES2Interface> gl);
 
   bool BindToCurrentThread() override;
   void DetachFromThread() override;
@@ -59,6 +61,7 @@ class TestContextProvider : public ContextProvider {
 
  protected:
   explicit TestContextProvider(
+      std::unique_ptr<TestGLES2Interface> gl,
       std::unique_ptr<TestWebGraphicsContext3D> context);
   ~TestContextProvider() override;