cc: Allow the main thread to cancel commits

cc/layers/layer.h

 // Copyright 2010 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.
 
 #ifndef CC_LAYERS_LAYER_H_
 #define CC_LAYERS_LAYER_H_
 
 #include <string>
 
 #include "base/callback.h"
@@ skipping 375 matching lines @@
     return num_dependents_need_push_properties_ > 0;
   }
 
  protected:
   friend class LayerImpl;
   friend class TreeSynchronizer;
   virtual ~Layer();
 
   Layer();
 
+  // These SetNeeds functions are in order of severity of update:
+  //
+  // Called when this layer has been modified in some way, but isn't sure
+  // that it needs a commit yet.  It needs CalcDrawProperties and UpdateLayers
+  // before it knows whether or not a commit is required.
+  void SetNeedsUpdate();
+  // Called when a property has been modified in a way that the layer
+  // knows immediately that a commit is required.  This implies SetNeedsUpdate
+  // as well as SetNeedsPushProperties to push that property.
   void SetNeedsCommit();
+  // Called when there's been a change in layer structure.  Implies both
+  // SetNeedsUpdate and SetNeedsCommit, but not SetNeedsPushProperties.
   void SetNeedsFullTreeSync();
   bool IsPropertyChangeAllowed() const;
 
   void SetNeedsPushProperties();
   void AddDependentNeedsPushProperties();
   void RemoveDependentNeedsPushProperties();
   bool parent_should_know_need_push_properties() const {
     return needs_push_properties() || descendant_needs_push_properties();
   }
 
@@ skipping 20 matching lines @@
   // outside the compositor's control (i.e. plugin layers), this information
   // is not available and the update rect will remain empty.
   // Note this rect is in layer space (not content space).
   gfx::RectF update_rect_;
 
   scoped_refptr<Layer> mask_layer_;
 
   int layer_id_;
 
   // When true, the layer is about to perform an update. Any commit requests
-  // will be handled implcitly after the update completes.
+  // will be handled implicitly after the update completes.
   bool ignore_set_needs_commit_;
 
  private:
   friend class base::RefCounted<Layer>;
 
   void SetParent(Layer* layer);
   bool HasAncestor(const Layer* ancestor) const;
   bool DescendantIsFixedToContainerLayer() const;
 
   // Returns the index of the child or -1 if not found.
@@ skipping 65 matching lines @@
   DrawProperties<Layer, RenderSurface> draw_properties_;
 
   PaintProperties paint_properties_;
 
   DISALLOW_COPY_AND_ASSIGN(Layer);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_LAYER_H_