Update from https://crrev.com/320343

cc/resources/pixel_ref_map.h

+// Copyright 2015 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_PIXEL_REF_MAP_H_
+#define CC_RESOURCES_PIXEL_REF_MAP_H_
+
+#include <utility>
+#include <vector>
+
+#include "base/containers/hash_tables.h"
+#include "base/lazy_instance.h"
+#include "base/memory/ref_counted.h"
+#include "cc/base/cc_export.h"
+#include "third_party/skia/include/core/SkPicture.h"
+#include "ui/gfx/geometry/rect.h"
+#include "ui/gfx/geometry/size.h"
+
+class SkPixelRef;
+
+namespace cc {
+
+class Picture;
+
+typedef std::pair<int, int> PixelRefMapKey;
+typedef std::vector<SkPixelRef*> PixelRefs;
+typedef base::hash_map<PixelRefMapKey, PixelRefs> PixelRefHashmap;
+
+// This class is used and owned by cc Picture class. It is used to gather pixel
+// refs which would happen after record. It takes in |cell_size| to decide how
+// big each grid cell should be.
+class CC_EXPORT PixelRefMap {
+ public:
+  explicit PixelRefMap(const gfx::Size& cell_size);
+  ~PixelRefMap();
+  void GatherPixelRefsFromPicture(SkPicture* picture);
+
+  bool empty() const { return data_hash_map_.empty(); }
+
+  // This iterator imprecisely returns the set of pixel refs that are needed to
+  // raster this layer rect from this picture.  Internally, pixel refs are
+  // clumped into tile grid buckets, so there may be false positives.
+  class CC_EXPORT Iterator {
+   public:
+    // Default iterator constructor that is used as place holder for invalid
+    // Iterator.
+    Iterator();
+    Iterator(const gfx::Rect& layer_rect, const Picture* picture);
+    ~Iterator();
+
+    SkPixelRef* operator->() const {
+      DCHECK_LT(current_index_, current_pixel_refs_->size());
+      return (*current_pixel_refs_)[current_index_];
+    }
+
+    SkPixelRef* operator*() const {
+      DCHECK_LT(current_index_, current_pixel_refs_->size());
+      return (*current_pixel_refs_)[current_index_];
+    }
+
+    Iterator& operator++();
+    operator bool() const {
+      return current_index_ < current_pixel_refs_->size();
+    }
+
+   private:
+    static base::LazyInstance<PixelRefs> empty_pixel_refs_;
+    const PixelRefMap* target_pixel_ref_map_;
+    const PixelRefs* current_pixel_refs_;
+    unsigned current_index_;
+
+    gfx::Rect layer_rect_;
+
+    gfx::Point min_point_;
+    gfx::Point max_point_;
+    int current_x_;
+    int current_y_;
+  };
+
+ private:
+  gfx::Point min_pixel_cell_;
+  gfx::Point max_pixel_cell_;
+  gfx::Size cell_size_;
+
+  PixelRefHashmap data_hash_map_;
+};
+
+}  // namespace cc
+
+#endif  // CC_RESOURCES_PIXEL_REF_MAP_H_