currentlyscrollinglayer cleared in scrollAnimatedBegin.

cc/trees/layer_tree_host_impl.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/layer_tree_host_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 2770 matching lines @@
     } else {
       scroll_status.thread = SCROLL_IGNORED;
       scroll_status.main_thread_scrolling_reasons =
           MainThreadScrollingReason::kNotScrollable;
     }
     return scroll_status;
   }
   ScrollStateData scroll_state_data;
   scroll_state_data.position_x = viewport_point.x();
   scroll_state_data.position_y = viewport_point.y();
-  scroll_state_data.is_in_inertial_phase = true;
+  scroll_state_data.is_in_inertial_phase = false;
   ScrollState scroll_state(scroll_state_data);
 
   // ScrollAnimated is used for animated wheel scrolls. We find the first layer
   // that can scroll and set up an animation of its scroll offset. Note that
   // this does not currently go through the scroll customization machinery
   // that ScrollBy uses for non-animated wheel scrolls.
   scroll_status = ScrollBegin(&scroll_state, WHEEL);
   scroll_node = scroll_tree.CurrentlyScrollingNode();
   if (scroll_status.thread == SCROLL_ON_IMPL_THREAD) {
     ScrollStateData scroll_state_end_data;
     scroll_state_end_data.is_ending = true;
     ScrollState scroll_state_end(scroll_state_end_data);
+    // TODO(Sahel): Once the touchpad scroll latching for Non-mac devices is
+    // impelemented, the current scrolling layer should not get cleared after

[tdresser, 2016/08/31 13:10:05]

implemented

[sahel, 2016/08/31 14:25:10]

Done.

+    // each animation (crbug.com/526463).
     ScrollEnd(&scroll_state_end);
+    ClearCurrentlyScrollingLayer();

[ymalik, 2016/08/31 14:01:55]

I suspect that this is working correctly now because of your change above
(scroll_state_data.is_in_inertial_phase = false) and not because of your call to
ClearCurrentlyScrollingLayer().

Can you verify that this is the case?

If so, please update the description to better explain this case. 
  

[sahel, 2016/08/31 14:25:09]

It is working because of the call. The problem was that after calling
animatedBegin once and not clearing the scrolling layer, the second time that
animatedBegin was called, it would fall on the part that scroll gets ignored and
return before calling scrollBegin.

Correcting the is_in_initial_phase value is for scrollBegin function. In the
scrollBegin if the is_in_inertial_phase is true fling code is called, and that's
why is_in_initial_phase should be iff true in the case of a fling.

   }
   return scroll_status;
 }
 
 gfx::Vector2dF LayerTreeHostImpl::ComputeScrollDelta(
     ScrollNode* scroll_node,
     const gfx::Vector2dF& delta) {
   ScrollTree& scroll_tree = active_tree()->property_trees()->scroll_tree;
   float scale_factor = active_tree()->current_page_scale_factor();
 
@@ skipping 1373 matching lines @@
   return task_runner_provider_->HasImplThread();
 }
 
 bool LayerTreeHostImpl::CommitToActiveTree() const {
   // In single threaded mode we skip the pending tree and commit directly to the
   // active tree.
   return !task_runner_provider_->HasImplThread();
 }
 
 }  // namespace cc