Move PixelRefMap and its Iterator out from Picture class

cc/resources/picture_pile_impl.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_RESOURCES_PICTURE_PILE_IMPL_H_
 #define CC_RESOURCES_PICTURE_PILE_IMPL_H_
 
 #include <map>
 #include <set>
 #include <vector>
 
 #include "base/time/time.h"
 #include "cc/base/cc_export.h"
 #include "cc/debug/rendering_stats_instrumentation.h"
 #include "cc/resources/picture_pile.h"
+#include "cc/resources/pixel_ref_map.h"
 #include "cc/resources/raster_source.h"
 #include "skia/ext/analysis_canvas.h"
 #include "skia/ext/refptr.h"
 
 class SkCanvas;
 class SkPicture;
 class SkPixelRef;
 
 namespace gfx {
 class Rect;
@@ skipping 52 matching lines @@
     SkPixelRef* operator*() const { return *pixel_ref_iterator_; }
     PixelRefIterator& operator++();
     operator bool() const { return pixel_ref_iterator_; }
 
    private:
     void AdvanceToTilePictureWithPixelRefs();
 
     const PicturePileImpl* picture_pile_;
     gfx::Rect layer_rect_;
     TilingData::Iterator tile_iterator_;
-    Picture::PixelRefIterator pixel_ref_iterator_;
+    PixelRefMapIterator pixel_ref_iterator_;
     std::set<const void*> processed_pictures_;
   };
 
  protected:
   friend class PicturePile;
   friend class PixelRefIterator;
 
   // TODO(vmpstr): Change this when pictures are split from invalidation info.
   using PictureMapKey = PicturePile::PictureMapKey;
   using PictureMap = PicturePile::PictureMap;
@@ skipping 49 matching lines @@
   bool CanRasterSlowTileCheck(const gfx::Rect& layer_rect) const;
 
   gfx::Rect PaddedRect(const PictureMapKey& key) const;
 
   DISALLOW_COPY_AND_ASSIGN(PicturePileImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_RESOURCES_PICTURE_PILE_IMPL_H_