cc: Remove vectors from tiling eviction tile iterator.

cc/layers/picture_layer_impl.h

Index: cc/layers/picture_layer_impl.h
diff --git a/cc/layers/picture_layer_impl.h b/cc/layers/picture_layer_impl.h
index d49205137510bd9d5f3bc57e89a785d42de65616..680eec445c4d7b1ffa6f5b168e57c735e3b6cd50 100644
--- a/cc/layers/picture_layer_impl.h
+++ b/cc/layers/picture_layer_impl.h
@@ -77,14 +77,25 @@ class CC_EXPORT PictureLayerImpl
     operator bool() const;
 
    private:
+    struct TilingIterationRange {
+      int start_index;
+      int one_past_end_index;
+    };
+
+    void ConstructRanges();
+    bool CurrentTilingIndexInRange();
     void AdvanceToNextIterator();
-    bool IsCorrectType(
-        PictureLayerTiling::TilingEvictionTileIterator* it) const;
+    bool AdvanceTiling();
+    bool AdvanceRange();
+    bool AdvanceStage();
 
-    std::vector<PictureLayerTiling::TilingEvictionTileIterator> iterators_;
-    size_t iterator_index_;
+    PictureLayerTiling::TilingEvictionTileIterator iterator_;
+    int tiling_index_;
     TilePriority::PriorityBin iteration_stage_;
+    TilingIterationRange ranges_[5];

[reveman, 2014/07/29 16:50:49]

Some enums representing each stage and each range might help make the code a bit
easier to read.

[vmpstr, 2014/07/29 17:08:49]

Ok, I will do this.

+    int range_index_;
     bool required_for_activation_;
+    TreePriority tree_priority_;
 
     PictureLayerImpl* layer_;
   };

[reveman, 2014/07/29 16:50:49]

If I understand this iterator correctly. This is what it does: it iterates
through all tiles, for each tiling of each range of each stage.

Seems like what we really have here is a number of iterators baked into one.
Would it be possible to separate this into different iterators. I think that
might make it easier to understand and reduce the complexity of the code a bit.
We'd have a StageIterator and a RangeIterator. Wdyt?

[vmpstr, 2014/07/29 17:08:49]

That's kind of what we have with AdvanceTiling/AdvanceRange/AdvanceStage.. Those
are the operator++ of the iterators you propose. Are you suggesting making this
an explicit separate class? My initial thought is that it's a bit of an
overkill, but I can try and see if it makes it better. Let me know if that's
what you meant.

[reveman, 2014/07/29 18:04:32]

Yea, that's what I was thinking. Maybe the RangeIterator should be a
TilingSet::EvictionTileIterator that takes a range.