Prevent create ScrollbarAnimationController for Mac Overlay Scrollbar

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 999efbfdbcfdf8762def9c2687b60f1d481fe800..290aaa29913935087e674cbd1d4ec6734c05530f 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -510,18 +510,18 @@ void LayerTreeImpl::PushPropertiesTo(LayerTreeImpl* target_tree) {
 }
 
 void LayerTreeImpl::HandleScrollbarShowRequestsFromMain() {
-  LayerTreeHostCommon::CallFunctionForEveryLayer(this, [this](
-                                                           LayerImpl* layer) {
-    if (!layer->needs_show_scrollbars())
-      return;
-    ScrollbarAnimationController* controller =
-        layer_tree_host_impl_->ScrollbarAnimationControllerForElementId(
-            layer->element_id());
-    if (controller) {
-      controller->DidRequestShowFromMainThread();
-      layer->set_needs_show_scrollbars(false);
-    }
-  });
+  LayerTreeHostCommon::CallFunctionForEveryLayer(
+      this, [this](LayerImpl* layer) {

[aelias_OOO_until_Jul13, 2017/06/02 22:02:23]

Please omit this unrelated whitespace change.

+        if (!layer->needs_show_scrollbars())
+          return;
+        ScrollbarAnimationController* controller =
+            layer_tree_host_impl_->ScrollbarAnimationControllerForElementId(
+                layer->element_id());
+        if (controller) {
+          controller->DidRequestShowFromMainThread();
+          layer->set_needs_show_scrollbars(false);
+        }
+      });
 }
 
 void LayerTreeImpl::MoveChangeTrackingToLayers() {
@@ -1705,7 +1705,17 @@ void LayerTreeImpl::RegisterScrollbar(ScrollbarLayerImplBase* scrollbar_layer) {
     scrollbar_ids.vertical = scrollbar_layer->id();
   }
 
-  if (IsActiveTree() && scrollbar_layer->is_overlay_scrollbar()) {
+// Because we assigned settings().scrollbar_animator = Android for default, Here
+// we check IsSolidColorScrollbarLayerImpl(mobile emulator) to prevent creating
+// ScrollbarAnimationController for Mac Overlay Scrollbar.
+#if defined(OS_MACOSX)

[aelias_OOO_until_Jul13, 2017/06/02 22:02:23]

Please find a way to avoid OS_MACOSX.  How about early-returning if either
NO_ANIMATOR or ANDROID_OVERLAY &&
!scrollbar_layer->IsSolidColorScrollbarLayerImpl()?

+  if (IsActiveTree() && scrollbar_layer->is_overlay_scrollbar() &&
+      settings().scrollbar_animator != LayerTreeSettings::NO_ANIMATOR &&
+      scrollbar_layer->IsSolidColorScrollbarLayerImpl()) {
+#else
+  if (IsActiveTree() && scrollbar_layer->is_overlay_scrollbar() &&
+      settings().scrollbar_animator != LayerTreeSettings::NO_ANIMATOR) {
+#endif
     layer_tree_host_impl_->RegisterScrollbarAnimationController(
         scroll_element_id, scrollbar_layer->Opacity());
   }