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..cfde3ea9f43e4dc962c16869bccd0dc35492db55 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_);
 }
@@ -206,8 +210,19 @@ bool PaintedScrollbarLayer::Update(ResourceUpdateQueue* queue,
   gfx::Rect scaled_track_rect = ScrollbarLayerRectToContentRect(
       track_layer_rect);
 
-  if (track_rect_.IsEmpty() || scaled_track_rect.IsEmpty())
+  if (track_rect_.IsEmpty() || scaled_track_rect.IsEmpty()) {
+    if (track_resource_ && thumb_resource_) {

[danakj, 2014/09/10 16:15:03]

&& seems wrong here, if the track is the only thing present, we still want to
free it when the track rect is empty? can you add a test case for this?

[MuVen, 2014/09/11 14:07:21]

Done.

+      track_resource_.reset();
+      thumb_resource_.reset();
+      SetNeedsPushProperties();
+    }

[MuVen, 2014/09/10 15:40:58]

To make it simple i have added the reset of the UIResources without having any
seperate function for this. 

Comments by Dana:
can you move this into the Update() method after calling this? I feel like this
method should only do what its name says. 

how about "ReleaseThumbAndMaybeTrack(bool release_track)" instead of an enum and
switch?

     return false;
+  }
+
+  if (!has_thumb_ && thumb_resource_) {
+    thumb_resource_.reset();
+    SetNeedsPushProperties();
+  }
 
   {
     base::AutoReset<bool> ignore_set_needs_commit(&ignore_set_needs_commit_,