cc: Early-out UpdateTilePriorities if the layer has no tilings

cc/layers/picture_layer_impl.cc

 // Copyright 2012 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/picture_layer_impl.h"
 
 #include <algorithm>
 
 #include "base/time.h"
 #include "cc/base/math_util.h"
@@ skipping 244 matching lines @@
   // better scheme would be to maintain a tighter visible_content_rect for the
   // finer tilings.
   CleanUpTilingsOnActiveLayer(seen_tilings);
 }
 
 void PictureLayerImpl::DumpLayerProperties(std::string*, int indent) const {
   // TODO(enne): implement me
 }
 
 void PictureLayerImpl::UpdateTilePriorities() {
+  if (!tilings_->num_tilings())
+    return;
+
   UpdateLCDTextStatus();
 
   int current_source_frame_number = layer_tree_impl()->source_frame_number();
   double current_frame_time =
       (layer_tree_impl()->CurrentFrameTime() - base::TimeTicks()).InSecondsF();
 
   gfx::Transform current_screen_space_transform = screen_space_transform();
 
   gfx::Rect viewport_in_content_space;
   gfx::Transform screen_to_layer(gfx::Transform::kSkipInitialization);
@@ skipping 628 matching lines @@
 scoped_ptr<base::Value> PictureLayerImpl::AsValue() const {
   scoped_ptr<base::DictionaryValue> state(new base::DictionaryValue());
   LayerImpl::AsValueInto(state.get());
 
   state->SetDouble("ideal_contents_scale", ideal_contents_scale_);
   state->Set("tilings", tilings_->AsValue().release());
   return state.PassAs<base::Value>();
 }
 
 }  // namespace cc