cc: Change TileManager iterators to be queues.

cc/resources/eviction_tile_priority_queue.h

Index: cc/resources/eviction_tile_priority_queue.h
diff --git a/cc/resources/eviction_tile_priority_queue.h b/cc/resources/eviction_tile_priority_queue.h
new file mode 100644
index 0000000000000000000000000000000000000000..a459193a6d5f7a1df69e5777e796fe89d3503230
--- /dev/null
+++ b/cc/resources/eviction_tile_priority_queue.h
@@ -0,0 +1,68 @@
+// 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_EVICTION_TILE_PRIORITY_QUEUE_H_
+#define CC_RESOURCES_EVICTION_TILE_PRIORITY_QUEUE_H_
+
+#include <utility>
+#include <vector>
+
+#include "cc/base/cc_export.h"
+#include "cc/layers/picture_layer_impl.h"
+#include "cc/resources/tile_priority.h"
+
+namespace cc {
+
+class CC_EXPORT EvictionTilePriorityQueue {
+ public:
+  EvictionTilePriorityQueue();
+  ~EvictionTilePriorityQueue();
+
+  void Build(const std::vector<PairedPictureLayer>& paired_layers,
+             TreePriority tree_priority);
+  void Reset();
+
+  void Pop();
+  bool IsEmpty() const;
+  Tile* Top();
+
+ private:
+  struct PairedPictureLayerQueue {
+    PairedPictureLayerQueue();
+    ~PairedPictureLayerQueue();
+
+    Tile* PeekTile(TreePriority tree_priority);
+    void PopTile(TreePriority tree_priority);

[reveman, 2014/07/18 21:08:05]

Pop/Top above but PeekTile/PopTile here. Is there a good reason for that or can
we make it consistent?

[vmpstr, 2014/07/18 23:18:13]

I've changed the name and added IsEmpty

+
+    PictureLayerImpl::LayerEvictionTileIterator* NextTileIterator(
+        TreePriority tree_priority);
+
+    PictureLayerImpl::LayerEvictionTileIterator active_iterator;
+    PictureLayerImpl::LayerEvictionTileIterator pending_iterator;
+
+    std::vector<Tile*> returned_shared_tiles;

[reveman, 2014/07/18 21:08:05]

Can you add a TODO here about possibly removing this vector?

[vmpstr, 2014/07/18 23:18:13]

Done.

+  };
+
+  class EvictionOrderComparator {
+   public:
+    explicit EvictionOrderComparator(TreePriority tree_priority);
+
+    bool operator()(PairedPictureLayerQueue* a,
+                    PairedPictureLayerQueue* b) const;
+
+   private:
+    TreePriority tree_priority_;
+  };

[reveman, 2014/07/18 21:08:05]

You can move this to .cc after removing |comparator_|. See comment below.

[vmpstr, 2014/07/18 23:18:13]

Done.

+
+  std::vector<PairedPictureLayerQueue> paired_queues_;
+  std::vector<PairedPictureLayerQueue*> queue_heap_;

[reveman, 2014/07/18 21:08:05]

I understand that this might be needed for good performance but let's just
heapify paired_queues_ for now and we can change this in a follow up with perf
data.

[vmpstr, 2014/07/18 23:18:13]

Done.

+  TreePriority tree_priority_;
+  EvictionOrderComparator comparator_;

[reveman, 2014/07/18 21:08:05]

Not obvious to me that caching this comparator is worthwhile. Let's just create
this when needed for now and we can change it in a follow up if needed.

[vmpstr, 2014/07/18 23:18:13]

Done.

+
+  DISALLOW_COPY_AND_ASSIGN(EvictionTilePriorityQueue);
+};
+
+}  // namespace cc
+
+#endif  // CC_RESOURCES_EVICTION_TILE_PRIORITY_QUEUE_H_