Show Overlay Scrollbar when GestureScrollUpdate

cc/trees/layer_tree_impl.cc

Index: cc/trees/layer_tree_impl.cc
diff --git a/cc/trees/layer_tree_impl.cc b/cc/trees/layer_tree_impl.cc
index 7c338a4f8ec0e094768027c90fdfaa58fddb2515..fbe2261e5cbd56ab6ed11a80d96e3ba3e6c3f8da 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -242,19 +242,20 @@ void LayerTreeImpl::UpdateScrollbars(int scroll_layer_id, int clip_layer_id) {
   }
 
   bool scrollbar_needs_animation = false;
+  bool clip_layer_size_did_change = false;
   bool scroll_layer_size_did_change = false;
   bool y_offset_did_change = false;
   for (ScrollbarLayerImplBase* scrollbar : ScrollbarsFor(scroll_layer_id)) {
     if (scrollbar->orientation() == HORIZONTAL) {
       scrollbar_needs_animation |= scrollbar->SetCurrentPos(current_offset.x());
-      scrollbar_needs_animation |=
+      scrollbar_needs_animation |= clip_layer_size_did_change |=

[bokan, 2017/02/27 23:34:17]

Nit: separate this into separate lines.

[chaopeng, 2017/02/28 01:51:12]

This is formatted by clang-format.

[bokan, 2017/02/28 14:16:07]

I mean separate statements. Turn it in to this:

clip_layer_size_did_change |= scrollbar->SetClipLayerLength(...);
scrollbar_needs_animation |= clip_layer_size_did_change;

           scrollbar->SetClipLayerLength(clip_size.width());
       scrollbar_needs_animation |= scroll_layer_size_did_change |=
           scrollbar->SetScrollLayerLength(scroll_size.width());
     } else {
       scrollbar_needs_animation |= y_offset_did_change |=
           scrollbar->SetCurrentPos(current_offset.y());
-      scrollbar_needs_animation |=
+      scrollbar_needs_animation |= clip_layer_size_did_change |=
           scrollbar->SetClipLayerLength(clip_size.height());
       scrollbar_needs_animation |= scroll_layer_size_did_change |=
           scrollbar->SetScrollLayerLength(scroll_size.height());
@@ -271,8 +272,14 @@ void LayerTreeImpl::UpdateScrollbars(int scroll_layer_id, int clip_layer_id) {
     ScrollbarAnimationController* controller =
         layer_tree_host_impl_->ScrollbarAnimationControllerForId(
             scroll_layer_id);
-    if (controller)
-      controller->DidScrollUpdate(scroll_layer_size_did_change);
+    if (!controller)
+      return;
+
+    if (clip_layer_size_did_change || scroll_layer_size_did_change) {
+      controller->DidResize();
+    } else {
+      controller->WillUpdateScroll();
+    }
   }
 }