cc: Add tiling raster tile iterators.

cc/base/tiling_data.cc

Index: cc/base/tiling_data.cc
diff --git a/cc/base/tiling_data.cc b/cc/base/tiling_data.cc
index b369dde08ed65200a945ae512a65b07fb13a6440..1de106c642904192d46fc8b7637fc1c6452a1528 100644
--- a/cc/base/tiling_data.cc
+++ b/cc/base/tiling_data.cc
@@ -272,6 +272,8 @@ TilingData::BaseIterator::BaseIterator(const TilingData* tiling_data)
       index_y_(-1) {
 }
 
+TilingData::Iterator::Iterator() : BaseIterator(NULL) { done(); }
+
 TilingData::Iterator::Iterator(const TilingData* tiling_data,
                                const gfx::Rect& tiling_rect)
     : BaseIterator(tiling_data),
@@ -409,6 +411,11 @@ TilingData::DifferenceIterator& TilingData::DifferenceIterator::operator++() {
   return *this;
 }
 
+TilingData::SpiralDifferenceIterator::SpiralDifferenceIterator()
+    : BaseIterator(NULL) {
+  done();
+}
+
 TilingData::SpiralDifferenceIterator::SpiralDifferenceIterator(
     const TilingData* tiling_data,
     const gfx::Rect& consider_rect,