Animated scroll shouldn't consume unhandled scrolls for OOPIFs.

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 3015 matching lines @@
       if (ScrollAnimationCreate(scroll_node, scroll_delta, delayed_by)) {
         scroll_animating_latched_node_id_ = scroll_node->id;
         return scroll_status;
       }
 
       pending_delta -= scroll_delta;
     }
   }
   scroll_state.set_is_ending(true);
   ScrollEnd(&scroll_state);
+  if (settings_.is_layer_tree_for_subframe) {

[bokan, 2017/04/11 16:23:13]

Should this be `is_layer_tree_for_subframe && scroll_status.thread ==
SCROLL_ON_IMPL_THREAD`? If ScrollBegin says we should scroll on main because of
MainThreadScrollingReasons, we shouldn't then switch it to ignore, right?

[wjmaclean, 2017/04/11 20:04:51]

Good catch, thanks.

+    // If we get to here, we shouldn't return SCROLL_ON_IMPL_THREAD as otherwise
+    // we'll mark the scroll as handled and the scroll won't bubble.
+    scroll_status.thread = SCROLL_IGNORED;

[bokan, 2017/04/11 16:23:14]

How does this work for non-animated scrolls? In the bug, creis@ says it's also
broken when touch scrolling - that doesn't use ScrollAnimated. Should we be
updating the non-animated path too?

[wjmaclean, 2017/04/11 20:04:51]

I haven't been able to reproduce the touch scrolling issue.

I think there *is* an issue with the current OOPIF scroll bubbling code if you
follow a mousewheel scroll that bubbles with a mainframe touch scroll ... I plan
on looking into that as a separate issue.

+    scroll_status.main_thread_scrolling_reasons =
+        MainThreadScrollingReason::kNotScrollable;
+  }
   return scroll_status;
 }
 
 gfx::Vector2dF LayerTreeHostImpl::ScrollNodeWithViewportSpaceDelta(
     ScrollNode* scroll_node,
     const gfx::PointF& viewport_point,
     const gfx::Vector2dF& viewport_delta,
     ScrollTree* scroll_tree) {
   // Layers with non-invertible screen space transforms should not have passed
   // the scroll hit test in the first place.
@@ skipping 1251 matching lines @@
 }
 
 void LayerTreeHostImpl::UpdateScrollSourceInfo(bool is_wheel_scroll) {
   if (is_wheel_scroll)
     has_scrolled_by_wheel_ = true;
   else
     has_scrolled_by_touch_ = true;
 }
 
 }  // namespace cc