Animated scroll shouldn't consume unhandled scrolls for OOPIFs.

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index 62654865f4d51e641bd820b3652b2b945f2c1adc..d57f318082212f3c04d4acf4a2e4c03cc4a77180 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -3033,6 +3033,13 @@ InputHandler::ScrollStatus LayerTreeHostImpl::ScrollAnimated(
   }
   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;
 }