Scroll with Layers in views::ScrollView

cc/trees/single_thread_proxy.cc

Index: cc/trees/single_thread_proxy.cc
diff --git a/cc/trees/single_thread_proxy.cc b/cc/trees/single_thread_proxy.cc
index 5b0fb57027e476c8eb01c62f718c3d1a2a639ce2..6e39997490f987671a362502cf7be8f43db48871 100644
--- a/cc/trees/single_thread_proxy.cc
+++ b/cc/trees/single_thread_proxy.cc
@@ -254,15 +254,6 @@ void SingleThreadProxy::DoCommit() {
             "461509 SingleThreadProxy::DoCommit7"));
     layer_tree_host_->FinishCommitOnImplThread(layer_tree_host_impl_.get());
 
-#if DCHECK_IS_ON()
-    // In the single-threaded case, the scale and scroll deltas should never be
-    // touched on the impl layer tree.
-    std::unique_ptr<ScrollAndScaleSet> scroll_info =
-        layer_tree_host_impl_->ProcessScrollDeltas();
-    DCHECK(scroll_info->scrolls.empty());
-    DCHECK_EQ(1.f, scroll_info->page_scale_delta);
-#endif
-
     if (scheduler_on_impl_thread_)
       scheduler_on_impl_thread_->DidCommit();
 
@@ -589,7 +580,7 @@ void SingleThreadProxy::CompositeImmediately(base::TimeTicks frame_begin_time) {
 }
 
 bool SingleThreadProxy::SupportsImplScrolling() const {
-  return false;
+  return false;  // TODO(tapted): Should this return true?

[Ian Vollick, 2016/08/09 14:00:49]

I think this should only return true if we're asynchronously scrolling; seems
correct for this to return false.

I hadn't seen this before and it looks like it's only used to detect when we'll
do impl-thread scroll animations. +ymalik in case I've got this wrong.

[tapted, 2016/08/10 05:39:04]

Done.

 }
 
 bool SingleThreadProxy::ShouldComposite() const {
@@ -802,6 +793,10 @@ void SingleThreadProxy::BeginMainFrame(const BeginFrameArgs& begin_frame_args) {
 
 void SingleThreadProxy::DoBeginMainFrame(
     const BeginFrameArgs& begin_frame_args) {
+  std::unique_ptr<ScrollAndScaleSet> scroll_info =
+      layer_tree_host_impl_->ProcessScrollDeltas();
+  layer_tree_host_->ApplyScrollAndScale(scroll_info.get());
+
   layer_tree_host_->WillBeginMainFrame();
   layer_tree_host_->BeginMainFrame(begin_frame_args);
   layer_tree_host_->AnimateLayers(begin_frame_args.frame_time);