cc: Implement tiling iterator based on pyramid sequence.

cc/base/spiral_iterator.h

Index: cc/base/spiral_iterator.h
diff --git a/cc/base/spiral_iterator.h b/cc/base/spiral_iterator.h
index d30176d0037d64833da90abf8021c060b5e80cc1..01b1f08f77f7d463264d71fd3b8d1c826db1f43c 100644
--- a/cc/base/spiral_iterator.h
+++ b/cc/base/spiral_iterator.h
@@ -33,8 +33,12 @@ class CC_EXPORT SpiralIterator {
   SpiralIterator(const IndexRect& around_index_rect,
                  const IndexRect& consider_index_rect,
                  const IndexRect& ignore_index_rect);
+  SpiralIterator(const SpiralIterator& other);
+  SpiralIterator(SpiralIterator&& other);
+  ~SpiralIterator();
 
-  ~SpiralIterator() = default;
+  SpiralIterator& operator=(const SpiralIterator& other);
+  SpiralIterator& operator=(SpiralIterator&& other);
 
   operator bool() const;
   SpiralIterator& operator++();