Integrating SkSurface with SkDeferredCanvas

include/core/SkSurface.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkSurface_DEFINED
 #define SkSurface_DEFINED
 
@@ skipping 63 matching lines @@
      *  method will return a new value.
      *
      *  If this surface is empty (i.e. has a zero-dimention), this will return
      *  0.
      */
     uint32_t generationID();
 
     /**
      *  Call this if the contents have changed. This will (lazily) force a new
      *  value to be returned from generationID() when it is called next.
+     *  @param canDiscardContents For performance, set to true when it is known
+     *      that the contents of the surface do not need to be preserved (e.g. 
+     *      because they will be overwritten).
      */
-    void notifyContentChanged();
+    void notifyContentChanged(bool canDiscardContents = false);
 
     /**
      *  Return a canvas that will draw into this surface. This will always
      *  return the same canvas for a given surface, and is manged/owned by the
      *  surface. It should not be used when its parent surface has gone out of
      *  scope.
      */
     SkCanvas* getCanvas();
 
     /**
@@ skipping 37 matching lines @@
 
 private:
     const int   fWidth;
     const int   fHeight;
     uint32_t    fGenerationID;
 
     typedef SkRefCnt INHERITED;
 };
 
 #endif