NOT FOR LANDING - [WebView] Allow fling animation via the LayerScrollOffsetDelegate

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 eddbc60b09655a7594d09a16f089205f8d945bee..99a480da692899741e180cd499500398e1ca5278 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -379,8 +379,11 @@ bool LayerTreeHostImpl::CanDraw() const {
 }
 
 void LayerTreeHostImpl::Animate(base::TimeTicks monotonic_time) {
-  if (input_handler_client_)
-    input_handler_client_->Animate(monotonic_time);
+  if (!root_layer_scroll_offset_delegate_ ||
+      (CurrentlyScrollingLayer() != InnerViewportScrollLayer() &&
+       CurrentlyScrollingLayer() != OuterViewportScrollLayer())) {
+    AnimateInput(monotonic_time);
+  }
   AnimatePageScale(monotonic_time);
   AnimateLayers(monotonic_time);
   AnimateScrollbars(monotonic_time);
@@ -439,6 +442,22 @@ void LayerTreeHostImpl::StartPageScaleAnimation(
   client_->RenewTreePriority();
 }
 
+void LayerTreeHostImpl::SetNeedsAnimateInput() {
+  if (root_layer_scroll_offset_delegate_ &&
+      (CurrentlyScrollingLayer() == InnerViewportScrollLayer() ||
+       CurrentlyScrollingLayer() == OuterViewportScrollLayer())) {
+    if (root_layer_animation_callback_.is_null()) {
+      root_layer_animation_callback_ =
+          base::Bind(&LayerTreeHostImpl::AnimateInput, AsWeakPtr());
+    }
+    root_layer_scroll_offset_delegate_->SetNeedsAnimate(
+        root_layer_animation_callback_);
+    return;
+  }
+
+  SetNeedsAnimate();
+}
+
 bool LayerTreeHostImpl::IsCurrentlyScrollingLayerAt(
     const gfx::Point& viewport_point,
     InputHandler::ScrollInputType type) {
@@ -2824,7 +2843,7 @@ InputHandler::ScrollStatus LayerTreeHostImpl::FlingScrollBegin() {
   if (!active_tree_->CurrentlyScrollingLayer())
     return SCROLL_IGNORED;
 
-  if (settings_.ignore_root_layer_flings &&
+  if (false && settings_.ignore_root_layer_flings &&
       (active_tree_->CurrentlyScrollingLayer() == InnerViewportScrollLayer() ||
        active_tree_->CurrentlyScrollingLayer() == OuterViewportScrollLayer())) {
     ClearCurrentlyScrollingLayer();
@@ -3065,6 +3084,13 @@ void LayerTreeHostImpl::ScrollViewportBy(gfx::Vector2dF scroll_delta) {
     InnerViewportScrollLayer()->ScrollBy(unused_delta);
 }
 
+void LayerTreeHostImpl::AnimateInput(base::TimeTicks monotonic_time) {
+  DCHECK(proxy_->IsImplThread());
+  // TODO(jdduke): Skip when scrolling the root layer with an offset delegate?
+  if (input_handler_client_)
+    input_handler_client_->Animate(monotonic_time);
+}
+
 void LayerTreeHostImpl::AnimatePageScale(base::TimeTicks monotonic_time) {
   if (!page_scale_animation_)
     return;