Picture Recording: fix the performance bottleneck in SkDeferredCanvas::isFullFrame

include/utils/SkDeferredCanvas.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 SkDeferredCanvas_DEFINED
 #define SkDeferredCanvas_DEFINED
 
@@ skipping 71 matching lines @@
      *  of the previous frame. For example, if a canvas is cleared before
      *  drawing each frame, the frames will all be considered fresh.
      *  A frame is defined as the graphics image produced by as a result
      *  of all the canvas draws operation executed between two successive
      *  calls to isFreshFrame.  The result of isFreshFrame is computed
      *  conservatively, so it may report false negatives.
      */
     bool isFreshFrame() const;
 
     /**
+     * Returns canvas's size.
+     */
+    SkISize getCanvasSize() const;
+
+    /**
      *  Returns true if the canvas has recorded draw commands that have
      *  not yet been played back.
      */
     bool hasPendingCommands() const;
 
     /**
      *  Flushes pending draw commands, if any, and returns an image of the
      *  current state of the surface pixels up to this point. Subsequent
      *  changes to the surface (by drawing into its canvas) will not be
      *  reflected in this image.  Will return NULL if the deferred canvas
@@ skipping 141 matching lines @@
     void recordedDrawCommand();
     SkCanvas* drawingCanvas() const;
     SkCanvas* immediateCanvas() const;
     bool isFullFrame(const SkRect*, const SkPaint*) const;
     void validate() const;
     void init();
 
     size_t fBitmapSizeThreshold;
     bool   fDeferredDrawing;
 
+    mutable SkISize fCachedCanvasSize;
+    mutable bool    fCachedCanvasSizeDirty;
+
     friend class SkDeferredCanvasTester; // for unit testing
     typedef SkCanvas INHERITED;
 };
 
 
 #endif