Disable overlay scrollbars in Blink when hidden by the compositor.

cc/layers/layer_impl.cc

 // Copyright 2012 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/layers/layer_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 64 matching lines @@
       effect_tree_index_(EffectTree::kInvalidNodeId),
       clip_tree_index_(ClipTree::kInvalidNodeId),
       scroll_tree_index_(ScrollTree::kInvalidNodeId),
       sorting_context_id_(0),
       current_draw_mode_(DRAW_MODE_NONE),
       mutable_properties_(MutableProperty::kNone),
       debug_info_(nullptr),
       has_preferred_raster_bounds_(false),
       scrolls_drawn_descendant_(false),
       has_will_change_transform_hint_(false),
-      needs_push_properties_(false) {
+      needs_push_properties_(false),
+      scrollbars_hidden_(false) {
   DCHECK_GT(layer_id_, 0);
 
   DCHECK(layer_tree_impl_);
   layer_tree_impl_->RegisterLayer(this);
   layer_tree_impl_->AddToElementMap(this);
 
   SetNeedsPushProperties();
 }
 
 LayerImpl::~LayerImpl() {
@@ skipping 252 matching lines @@
   layer->background_color_ = background_color_;
   layer->safe_opaque_background_color_ = safe_opaque_background_color_;
   layer->draw_blend_mode_ = draw_blend_mode_;
   layer->position_ = position_;
   layer->transform_tree_index_ = transform_tree_index_;
   layer->effect_tree_index_ = effect_tree_index_;
   layer->clip_tree_index_ = clip_tree_index_;
   layer->scroll_tree_index_ = scroll_tree_index_;
   layer->sorting_context_id_ = sorting_context_id_;
   layer->has_will_change_transform_hint_ = has_will_change_transform_hint_;
+  layer->scrollbars_hidden_ = scrollbars_hidden_;
 
   if (layer_property_changed_) {
     layer->layer_tree_impl()->set_needs_update_draw_properties();
     layer->layer_property_changed_ = true;
   }
 
   // If whether layer has render surface changes, we need to update draw
   // properties.
   // TODO(weiliangc): Should be safely removed after impl side is able to
   // update render surfaces without rebuilding property trees.
@@ skipping 729 matching lines @@
            .layer_transforms_should_scale_layer_contents) {
     return default_scale;
   }
 
   gfx::Vector2dF transform_scales = MathUtil::ComputeTransform2dScaleComponents(
       ScreenSpaceTransform(), default_scale);
   return std::max(transform_scales.x(), transform_scales.y());
 }
 
 }  // namespace cc