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

include/utils/SkDeferredCanvas.h

Index: include/utils/SkDeferredCanvas.h
diff --git a/include/utils/SkDeferredCanvas.h b/include/utils/SkDeferredCanvas.h
index 907cb91575043b1cfba2f16c1b27e4d6982c0516..5f781f88594e4fb48ece47189ff37bd80dddc5d6 100644
--- a/include/utils/SkDeferredCanvas.h
+++ b/include/utils/SkDeferredCanvas.h
@@ -89,6 +89,11 @@ public:
     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.
      */
@@ -250,6 +255,9 @@ private:
     size_t fBitmapSizeThreshold;
     bool   fDeferredDrawing;
 
+    mutable SkISize fCachedCanvasSize;
+    mutable bool    fCachedCanvasSizeDirty;
+
     friend class SkDeferredCanvasTester; // for unit testing
     typedef SkCanvas INHERITED;
 };