Prevent create ScrollbarAnimationController for Mac Overlay Scrollbar

cc/trees/layer_tree_impl.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/trees/layer_tree_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 492 matching lines @@
   else
     target_tree->set_hud_layer(NULL);
 
   target_tree->has_ever_been_drawn_ = false;
 
   // Note: this needs to happen after SetPropertyTrees.
   target_tree->HandleScrollbarShowRequestsFromMain();
 }
 
 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() {
   // We need to update the change tracking on property trees before we move it
   // onto the layers.
   property_trees_.UpdateChangeTracking();
   for (auto* layer : *this) {
     if (layer->LayerPropertyChanged())
       layer->NoteLayerPropertyChanged();
   }
@@ skipping 1163 matching lines @@
   if (scrollbar_layer->orientation() == HORIZONTAL) {
     DCHECK_EQ(scrollbar_ids.horizontal, Layer::INVALID_ID)
         << "Existing scrollbar should have been unregistered.";
     scrollbar_ids.horizontal = scrollbar_layer->id();
   } else {
     DCHECK_EQ(scrollbar_ids.vertical, Layer::INVALID_ID)
         << "Existing scrollbar should have been unregistered.";
     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());
   }
 
   // TODO(pdr): Refactor DidUpdateScrollState to use ElementIds instead of
   // layer ids and remove this use of LayerIdByElementId.
   DidUpdateScrollState(LayerIdByElementId(scroll_element_id));
 }
 
 void LayerTreeImpl::UnregisterScrollbar(
@@ skipping 413 matching lines @@
 
 void LayerTreeImpl::ResetAllChangeTracking() {
   layers_that_should_push_properties_.clear();
   // Iterate over all layers, including masks.
   for (auto& layer : *layers_)
     layer->ResetChangeTracking();
   property_trees_.ResetAllChangeTracking();
 }
 
 }  // namespace cc