Scroll with Layers in views::ScrollView

cc/trees/single_thread_proxy.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/trees/single_thread_proxy.h"
 
 #include "base/auto_reset.h"
 #include "base/memory/ptr_util.h"
 #include "base/profiler/scoped_tracker.h"
 #include "base/trace_event/trace_event.h"
@@ skipping 236 matching lines @@
     if (layer_tree_host_impl_->EvictedUIResourcesExist())
       layer_tree_host_->RecreateUIResources();
 
     // TODO(robliao): Remove ScopedTracker below once https://crbug.com/461509
     // is fixed.
     tracked_objects::ScopedTracker tracking_profile7(
         FROM_HERE_WITH_EXPLICIT_FUNCTION(
             "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();
 
     layer_tree_host_impl_->CommitComplete();
 
     // TODO(robliao): Remove ScopedTracker below once https://crbug.com/461509
     // is fixed.
     tracked_objects::ScopedTracker tracking_profile8(
         FROM_HERE_WITH_EXPLICIT_FUNCTION(
             "461509 SingleThreadProxy::DoCommit8"));
@@ skipping 306 matching lines @@
     // DoComposite could abort, but because this is a synchronous composite
     // another draw will never be scheduled, so break remaining promises.
     layer_tree_host_impl_->active_tree()->BreakSwapPromises(
         SwapPromise::SWAP_FAILS);
 
     DidFinishImplFrame();
   }
 }
 
 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 {
   DCHECK(task_runner_provider_->IsImplThread());
   return layer_tree_host_impl_->visible() &&
          layer_tree_host_impl_->CanDraw();
 }
 
 void SingleThreadProxy::ScheduleRequestNewOutputSurface() {
   if (output_surface_creation_callback_.IsCancelled() &&
@@ skipping 192 matching lines @@
   // Prevent new commits from being requested inside DoBeginMainFrame.
   // Note: We do not want to prevent SetNeedsAnimate from requesting
   // a commit here.
   commit_requested_ = true;
 
   DoBeginMainFrame(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);
   layer_tree_host_->RequestMainFrameUpdate();
 
   // New commits requested inside UpdateLayers should be respected.
   commit_requested_ = false;
 
   layer_tree_host_->UpdateLayers();
 
@@ skipping 68 matching lines @@
 void SingleThreadProxy::DidFinishImplFrame() {
   layer_tree_host_impl_->DidFinishImplFrame();
 #if DCHECK_IS_ON()
   DCHECK(inside_impl_frame_)
       << "DidFinishImplFrame called while not inside an impl frame!";
   inside_impl_frame_ = false;
 #endif
 }
 
 }  // namespace cc