Disable overlay scrollbars in Blink when hidden by the compositor.

cc/trees/layer_tree_host_in_process.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_in_process.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 850 matching lines @@
 
   if (layer_tree_->root_layer()) {
     for (size_t i = 0; i < info->scrolls.size(); ++i) {
       Layer* layer = layer_tree_->LayerById(info->scrolls[i].layer_id);
       if (!layer)
         continue;
       layer->SetScrollOffsetFromImplSide(gfx::ScrollOffsetWithDelta(
           layer->scroll_offset(), info->scrolls[i].scroll_delta));
       SetNeedsUpdateLayers();
     }
+    for (size_t i = 0; i < info->scrollbars.size(); ++i) {
+      Layer* layer = layer_tree_->LayerById(info->scrollbars[i].layer_id);
+      if (!layer)
+        continue;
+      layer->SetScrollbarsHiddenFromImplSide(info->scrollbars[i].hidden);
+    }
   }
 
   // This needs to happen after scroll deltas have been sent to prevent top
   // controls from clamping the layout viewport both on the compositor and
   // on the main thread.
   ApplyViewportDeltas(info);
 }
 
 const base::WeakPtr<InputHandler>& LayerTreeHostInProcess::GetInputHandler()
     const {
@@ skipping 142 matching lines @@
 
   debug_state_.FromProtobuf(proto.debug_state());
   has_gpu_rasterization_trigger_ = proto.has_gpu_rasterization_trigger();
   content_is_suitable_for_gpu_rasterization_ =
       proto.content_is_suitable_for_gpu_rasterization();
   id_ = proto.id();
   next_commit_forces_redraw_ = proto.next_commit_forces_redraw();
 }
 
 }  // namespace cc