cc: Move LayerRasterTileIterator to a separate file and make it a queue

cc/resources/tiling_set_raster_queue.h

+// Copyright 2014 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_TILING_SET_RASTER_QUEUE_H_
+#define CC_RESOURCES_TILING_SET_RASTER_QUEUE_H_
+
+#include "cc/base/cc_export.h"
+#include "cc/resources/picture_layer_tiling_set.h"
+
+namespace cc {
+
+class CC_EXPORT TilingSetRasterQueue {
+ public:
+  TilingSetRasterQueue();
+  TilingSetRasterQueue(PictureLayerTilingSet* tiling_set,
+                       bool prioritize_low_res);
+  ~TilingSetRasterQueue();
+
+  Tile* Top();
+  const Tile* Top() const;
+  void Pop();
+  bool IsEmpty() const;
+
+ private:
+  enum IteratorType { LOW_RES, HIGH_RES, NUM_ITERATORS };
+
+  void AdvanceToNextStage();
+
+  PictureLayerTilingSet* tiling_set_;
+
+  struct IterationStage {
+    IteratorType iterator_type;
+    TilePriority::PriorityBin tile_type;
+  };
+
+  size_t current_stage_;
+
+  // One low res stage, and three high res stages.
+  IterationStage stages_[4];
+  PictureLayerTiling::TilingRasterTileIterator iterators_[NUM_ITERATORS];
+};
+
+}  // namespace cc
+
+#endif  // CC_RESOURCES_TILING_SET_RASTER_QUEUE_H_