Releasing Track & Thumb UIResources based on their Geometry

cc/layers/painted_scrollbar_layer.cc

 // Copyright 2013 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/layers/painted_scrollbar_layer.h"
 
 #include "base/auto_reset.h"
 #include "base/basictypes.h"
 #include "base/debug/trace_event.h"
 #include "cc/layers/painted_scrollbar_layer_impl.h"
@@ skipping 112 matching lines @@
         track_rect_.x() - location_.x());
     scrollbar_layer->SetTrackLength(track_rect_.width());
   } else {
     scrollbar_layer->SetTrackStart(
         track_rect_.y() - location_.y());
     scrollbar_layer->SetTrackLength(track_rect_.height());
   }
 
   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_);
 }
 
 ScrollbarLayerInterface* PaintedScrollbarLayer::ToScrollbarLayer() {
   return this;
 }
 
 void PaintedScrollbarLayer::PushScrollClipPropertiesTo(LayerImpl* layer) {
   PaintedScrollbarLayerImpl* scrollbar_layer =
@@ skipping 44 matching lines @@
   UpdateProperty(scrollbar_->Location(), &location_);
   UpdateProperty(scrollbar_->IsOverlay(), &is_overlay_);
   UpdateProperty(scrollbar_->HasThumb(), &has_thumb_);
   if (has_thumb_) {
     UpdateProperty(scrollbar_->ThumbThickness(), &thumb_thickness_);
     UpdateProperty(scrollbar_->ThumbLength(), &thumb_length_);
   } else {
     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,
                                    const OcclusionTracker<Layer>* occlusion) {
   UpdateThumbAndTrackGeometry();
 
   gfx::Rect track_layer_rect = gfx::Rect(location_, bounds());
   gfx::Rect scaled_track_rect = ScrollbarLayerRectToContentRect(
       track_layer_rect);
 
@@ skipping 57 matching lines @@
 
   scrollbar_->PaintPart(&skcanvas, part, layer_rect);
   // Make sure that the pixels are no longer mutable to unavoid unnecessary
   // allocation and copying.
   skbitmap.setImmutable();
 
   return UIResourceBitmap(skbitmap);
 }
 
 }  // namespace cc