[cc] Tiles and tile manager for impl side painting

cc/tile_priority.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_TILE_PRIORTY_H_
+#define CC_TILE_PRIORTY_H_
+
+#include "base/memory/ref_counted.h"
+#include "cc/picture_pile.h"
+#include "cc/tile_priority.h"
+#include "ui/gfx/rect.h"
+#include "ui/gfx/size.h"
+
+namespace cc {
+
+struct TilePriority {
+  // A given layer may have multiple tilings, of differing quality.
+  // would_be_drawn is set for the tiles that are visible that would be
+  // drawn if they were chosen.
+  bool would_be_drawn;
+
+  // Set to true for tiles that should be favored during, for example,
+  // scrolls.
+  bool on_primary_tree;
+
+  // Used to prefer tiles near to the viewport.
+  float distance_to_viewport;
+
+  // TODO(enne): some metric that penalizes blurriness.
+};
+
+class TilePriorityComparator {
+ public:
+  TilePriorityComparator(bool currently_scrolling)
+   : currently_scrolling_(currently_scrolling) {}
+
+  int compare(const TilePriority& a, const TilePriority& b) {
+    // TODO(nduca,enne): Implement a comparator using the attributes here.
+    return 0;
+  }
+
+ private:
+  bool currently_scrolling_;
+};
+
+}  // namespace cc
+#endif