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..b372ff480384d665cffc43fb886fd4aeddd44ed0 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_);
 }
@@ -205,9 +209,24 @@ bool PaintedScrollbarLayer::Update(ResourceUpdateQueue* queue,
   gfx::Rect track_layer_rect = gfx::Rect(location_, bounds());
   gfx::Rect scaled_track_rect = ScrollbarLayerRectToContentRect(
       track_layer_rect);
+  bool needs_update = false;

[danakj, 2014/09/11 20:12:56]

nit: updated

[MuVen, 2014/09/12 14:09:12]

Done.

+  if (track_rect_.IsEmpty() || scaled_track_rect.IsEmpty()) {
+    if (track_resource_) {
+      track_resource_.reset();
+      if (thumb_resource_)
+        thumb_resource_.reset();
+      SetNeedsPushProperties();
+      needs_update = true;
+    }
+    return needs_update;
+  }
 
-  if (track_rect_.IsEmpty() || scaled_track_rect.IsEmpty())
-    return false;
+  if (!has_thumb_ && thumb_resource_) {
+    thumb_resource_.reset();
+    SetNeedsPushProperties();
+    needs_update = true;
+    return needs_update;

[danakj, 2014/09/11 20:12:56]

not supposed to return here, you have a track rect and may need to update it.

[MuVen, 2014/09/12 14:09:12]

Done.
On 2014/09/11 20:12:56, danakj wrote:

+  }
 
   {
     base::AutoReset<bool> ignore_set_needs_commit(&ignore_set_needs_commit_,
@@ -216,7 +235,7 @@ bool PaintedScrollbarLayer::Update(ResourceUpdateQueue* queue,
   }
 
   if (update_rect_.IsEmpty() && track_resource_)
-    return false;
+    return needs_update;
 
   track_resource_ = ScopedUIResource::Create(
       layer_tree_host(),
@@ -233,7 +252,8 @@ bool PaintedScrollbarLayer::Update(ResourceUpdateQueue* queue,
 
   // UI resources changed so push properties is needed.
   SetNeedsPushProperties();
-  return true;
+  needs_update = true;
+  return needs_update;
 }
 
 UIResourceBitmap PaintedScrollbarLayer::RasterizeScrollbarPart(