Disable overlay scrollbars in Blink when hidden by the compositor.

cc/trees/layer_tree_host_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_host_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 2197 matching lines @@
   TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("compositor-worker"),
                "LayerTreeHostImpl::SetLayerTreeMutator");
   mutator_ = std::move(mutator);
   mutator_->SetClient(this);
 }
 
 LayerImpl* LayerTreeHostImpl::ViewportMainScrollLayer() {
   return viewport()->MainScrollLayer();
 }
 
+void LayerTreeHostImpl::DidChangeScrollbarVisibility() {
+  client_->SetNeedsCommitOnImplThread();
+}
+
 void LayerTreeHostImpl::CleanUpTileManagerAndUIResources() {
   ClearUIResources();
   tile_manager_.FinishTasksAndCleanUp();
   resource_pool_ = nullptr;
   single_thread_synchronous_task_graph_runner_ = nullptr;
   image_decode_controller_ = nullptr;
 
   // We've potentially just freed a large number of resources on our various
   // contexts. Flushing now helps ensure these are cleaned up quickly
   // preventing driver cache growth. See crbug.com/643251
@@ skipping 1108 matching lines @@
 static void CollectScrollDeltas(ScrollAndScaleSet* scroll_info,
                                 LayerTreeImpl* tree_impl) {
   if (tree_impl->LayerListIsEmpty())
     return;
 
   int inner_viewport_layer_id =
       tree_impl->InnerViewportScrollLayer()
           ? tree_impl->InnerViewportScrollLayer()->id()
           : Layer::INVALID_ID;
 
-  return tree_impl->property_trees()->scroll_tree.CollectScrollDeltas(
+  tree_impl->property_trees()->scroll_tree.CollectScrollDeltas(
       scroll_info, inner_viewport_layer_id);
 }
 
+static void CollectScrollbarUpdates(
+    ScrollAndScaleSet* scroll_info,
+    std::unordered_map<int, std::unique_ptr<ScrollbarAnimationController>>*
+        controllers) {
+  scroll_info->scrollbars.reserve(controllers->size());
+  for (auto& pair : *controllers) {
+    scroll_info->scrollbars.push_back(LayerTreeHostCommon::ScrollbarsUpdateInfo(
+        pair.first, pair.second->ScrollbarsHidden()));
+  }
+}
+
 std::unique_ptr<ScrollAndScaleSet> LayerTreeHostImpl::ProcessScrollDeltas() {
   std::unique_ptr<ScrollAndScaleSet> scroll_info(new ScrollAndScaleSet());
 
   CollectScrollDeltas(scroll_info.get(), active_tree_.get());
+  CollectScrollbarUpdates(scroll_info.get(), &scrollbar_animation_controllers_);
   scroll_info->page_scale_delta =
       active_tree_->page_scale_factor()->PullDeltaForMainThread();
   scroll_info->top_controls_delta =
       active_tree()->top_controls_shown_ratio()->PullDeltaForMainThread();
   scroll_info->elastic_overscroll_delta =
       active_tree_->elastic_overscroll()->PullDeltaForMainThread();
   scroll_info->swap_promises.swap(swap_promises_for_main_thread_scroll_update_);
 
   return scroll_info;
 }
@@ skipping 717 matching lines @@
   if (is_visible) {
     worker_context_visibility_ =
         worker_context->CacheController()->ClientBecameVisible();
   } else {
     worker_context->CacheController()->ClientBecameNotVisible(
         std::move(worker_context_visibility_));
   }
 }
 
 }  // namespace cc