Releasing Track & Thumb UIResources based on their Geometry

cc/layers/painted_scrollbar_layer.cc

Index: cc/layers/painted_scrollbar_layer.cc
diff --git a/cc/layers/painted_scrollbar_layer.cc b/cc/layers/painted_scrollbar_layer.cc
index 7062bc1e9bade7910cde353e5be9697cd9922e80..9208bfcce04f5f6c630b48864e153db2b756a001 100644
--- a/cc/layers/painted_scrollbar_layer.cc
+++ b/cc/layers/painted_scrollbar_layer.cc
@@ -130,8 +130,12 @@ void PaintedScrollbarLayer::PushPropertiesTo(LayerImpl* layer) {
 
   if (track_resource_.get())
     scrollbar_layer->set_track_ui_resource_id(track_resource_->id());
+  else
+    scrollbar_layer->set_track_ui_resource_id(0);
   if (thumb_resource_.get())
     scrollbar_layer->set_thumb_ui_resource_id(thumb_resource_->id());
+  else
+    scrollbar_layer->set_thumb_ui_resource_id(0);
 
   scrollbar_layer->set_is_overlay_scrollbar(is_overlay_);
 }
@@ -196,6 +200,17 @@ void PaintedScrollbarLayer::UpdateThumbAndTrackGeometry() {
     UpdateProperty(0, &thumb_thickness_);
     UpdateProperty(0, &thumb_length_);
   }
+  ReleaseThumbAndTrackUIResourcesIfNecessary();
+}
+
+void PaintedScrollbarLayer::ReleaseThumbAndTrackUIResourcesIfNecessary() {
+  if (track_rect_.IsEmpty() && track_resource_) {
+    track_resource_.reset();
+    SetNeedsPushProperties();
+  } else if ((!has_thumb_ || track_rect_.IsEmpty()) && thumb_resource_) {
+    thumb_resource_.reset();
+    SetNeedsPushProperties();

[danakj, 2014/09/04 16:38:10]

these need to make Update() return true also, so I think this needs to integrate
with the Update() early outs.

Also, tests for this?

[MuVen, 2014/09/05 14:44:13]

Done.Tests Added.

+  }
 }
 
 bool PaintedScrollbarLayer::Update(ResourceUpdateQueue* queue,