Disable overlay scrollbars in Blink when hidden by the compositor.

cc/trees/layer_tree_host_in_process.cc

Index: cc/trees/layer_tree_host_in_process.cc
diff --git a/cc/trees/layer_tree_host_in_process.cc b/cc/trees/layer_tree_host_in_process.cc
index 3affe069842af05187e80bd08b2ef45ec024d4a9..ac9c41a199db4cd87ebd91a1a9d2005c5a1d79ea 100644
--- a/cc/trees/layer_tree_host_in_process.cc
+++ b/cc/trees/layer_tree_host_in_process.cc
@@ -868,6 +868,12 @@ void LayerTreeHostInProcess::ApplyScrollAndScale(ScrollAndScaleSet* info) {
           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