cc: Implement tiling iterator based on pyramid sequence.

cc/base/spiral_iterator.cc

Index: cc/base/spiral_iterator.cc
diff --git a/cc/base/spiral_iterator.cc b/cc/base/spiral_iterator.cc
index 7d7387bd55e1d5f9bde0a61134af06cf39cc8be7..21eeb53958c670bccd89e5d65a06209cd3d24665 100644
--- a/cc/base/spiral_iterator.cc
+++ b/cc/base/spiral_iterator.cc
@@ -41,6 +41,20 @@ SpiralIterator::SpiralIterator(const IndexRect& around_index_rect,
   ++(*this);
 }
 
+SpiralIterator::SpiralIterator(const SpiralIterator::SpiralIterator& other) =
+    default;
+
+SpiralIterator::SpiralIterator(SpiralIterator::SpiralIterator&& other) =
+    default;
+
+SpiralIterator::~SpiralIterator() = default;
+
+SpiralIterator& SpiralIterator::operator=(
+    const SpiralIterator::SpiralIterator& other) = default;
+
+SpiralIterator& SpiralIterator::operator=(
+    SpiralIterator::SpiralIterator&& other) = default;
+
 SpiralIterator::operator bool() const {
   return index_x_ != -1 && index_y_ != -1;
 }