Let LayerTreeHostImpl::ScrollAnimated scroll the outer viewport.

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 2449788df4e23896abf10b90806008792ad85054..a245975db1f20bbe738e63786e40bde546ffed5c 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -2396,6 +2396,14 @@ LayerImpl* LayerTreeHostImpl::FindScrollLayerForDeviceViewportPoint(
   if (potentially_scrolling_layer_impl == OuterViewportScrollLayer())
     potentially_scrolling_layer_impl = InnerViewportScrollLayer();
 
+  // Animated wheel scrolls need to scroll the outer viewport layer, and do not
+  // go through Viewport::ScrollBy which would normally handle the distribution.
+  // NOTE: This will need refactoring if we want smooth scrolling on Android.
+  if (type == ANIMATED_WHEEL &&
+      potentially_scrolling_layer_impl == InnerViewportScrollLayer()) {
+    potentially_scrolling_layer_impl = OuterViewportScrollLayer();

[ymalik, 2015/10/19 22:36:54]

Instead of adding a new ScrollInputType, I wonder if its better to just check
for the smooth_scroll_enabled_ flag in the parent InputHandler class. That will
save use from doing Type = WHEEL || Type=ANIMATED_WHEEL every time. WDTY?

+  }
+
   return potentially_scrolling_layer_impl;
 }
 
@@ -2419,7 +2427,7 @@ InputHandler::ScrollStatus LayerTreeHostImpl::ScrollBeginImpl(
   top_controls_manager_->ScrollBegin();
 
   active_tree_->SetCurrentlyScrollingLayer(scrolling_layer_impl);
-  wheel_scrolling_ = (type == WHEEL);
+  wheel_scrolling_ = (type == WHEEL || type == ANIMATED_WHEEL);
   client_->RenewTreePriority();
   UMA_HISTOGRAM_BOOLEAN("TryScroll.SlowScroll", false);
   return SCROLL_STARTED;
@@ -2480,13 +2488,13 @@ InputHandler::ScrollStatus LayerTreeHostImpl::ScrollAnimated(
   // ScrollAnimated is only used for wheel scrolls. We use the same bubbling
   // behavior as ScrollBy to determine which layer to animate, but we do not
   // do the Android-specific things in ScrollBy like showing top controls.
-  InputHandler::ScrollStatus scroll_status = ScrollBegin(viewport_point, WHEEL);
+  InputHandler::ScrollStatus scroll_status =
+      ScrollBegin(viewport_point, ANIMATED_WHEEL);
   if (scroll_status == SCROLL_STARTED) {
     gfx::Vector2dF pending_delta = scroll_delta;
     for (LayerImpl* layer_impl = CurrentlyScrollingLayer(); layer_impl;
          layer_impl = NextLayerInScrollOrder(layer_impl)) {
-      // The inner viewport layer represents the viewport.
-      if (!layer_impl->scrollable() || layer_impl == OuterViewportScrollLayer())
+      if (!layer_impl->scrollable())
         continue;
 
       gfx::ScrollOffset current_offset = layer_impl->CurrentScrollOffset();