Implementation for cc::Picture::IsCheapInRect().

cc/picture.h

 // 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.
 
 #ifndef CC_PICTURE_H_
 #define CC_PICTURE_H_
 
 #include <list>
 
 #include "base/basictypes.h"
@@ skipping 24 matching lines @@
   // Record a paint operation. To be able to safely use this SkPicture for
   // playback on a different thread this can only be called once.
   void Record(ContentLayerClient*, RenderingStats*);
 
   // Has Record() been called yet?
   bool HasRecording() const { return picture_.get() != NULL; }
 
   // Apply this contents scale and raster the content rect into the canvas.
   void Raster(SkCanvas* canvas, gfx::Rect content_rect, float contents_scale);
 
+  // Estimate the cost of rasterizing. To predict the cost of a particular
+  // call to Raster(), pass this the bounds of the canvas that will
+  // be rastered into.
   bool IsCheapInRect(const gfx::Rect& layer_rect);
 
   void GatherPixelRefs(
       const gfx::Rect& layer_rect,
       std::list<skia::LazyPixelRef*>& pixel_ref_list);
 
  private:
   Picture(gfx::Rect layer_rect);
   // This constructor assumes SkPicture is already ref'd and transfers
   // ownership to this picture.
   Picture(const skia::RefPtr<SkPicture>&,
           gfx::Rect layer_rect,
           gfx::Rect opaque_rect);
   ~Picture();
 
   gfx::Rect layer_rect_;
   gfx::Rect opaque_rect_;
   skia::RefPtr<SkPicture> picture_;
 
   friend class base::RefCountedThreadSafe<Picture>;
   DISALLOW_COPY_AND_ASSIGN(Picture);
 };
 
 }  // namespace cc
 
 #endif  // CC_PICTURE_H_