CC Animations: Port Impl-only-scrolling to use compositor animation timelines.

cc/test/fake_proxy.cc

Index: cc/test/fake_proxy.cc
diff --git a/cc/test/fake_proxy.cc b/cc/test/fake_proxy.cc
index be1c22bb367de4edea15aee49bc0f3779831bfac..e37e144cb53fef70fb62df48dceaf6080b7cf532 100644
--- a/cc/test/fake_proxy.cc
+++ b/cc/test/fake_proxy.cc
@@ -28,7 +28,9 @@ bool FakeProxy::BeginMainFrameRequested() const { return false; }
 
 bool FakeProxy::CommitRequested() const { return false; }
 
-bool FakeProxy::SupportsImplScrolling() const { return false; }
+bool FakeProxy::SupportsImplScrolling() const {
+  return true;
+}
 
 bool FakeProxy::MainFrameWillHappenForTesting() {
   return false;