cc: Add const versions of operator* to layer iterators.

This patch adds const versions of operator* for layer iterators, so
that we can use them for sorting/heapifying the iterators.

R=reveman

Review URL: https://codereview.chromium.org/413603002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@285038 0039d316-1c4b-4281-b951-d872f2087c98

cc/layers/picture_layer_impl.cc

@@ -1508,6 +1508,16 @@ Tile* PictureLayerImpl::LayerRasterTileIterator::operator*() {
   return *iterators_[index];
 }
 
+const Tile* PictureLayerImpl::LayerRasterTileIterator::operator*() const {
+  DCHECK(*this);
+
+  IteratorType index = stages_[current_stage_].iterator_type;
+  DCHECK(iterators_[index]);
+  DCHECK(iterators_[index].get_type() == stages_[current_stage_].tile_type);
+
+  return *iterators_[index];
+}
+
 PictureLayerImpl::LayerEvictionTileIterator::LayerEvictionTileIterator()
     : iterator_index_(0),
       iteration_stage_(TilePriority::EVENTUALLY),
@@ -1585,6 +1595,11 @@ Tile* PictureLayerImpl::LayerEvictionTileIterator::operator*() {
   return *iterators_[iterator_index_];
 }
 
+const Tile* PictureLayerImpl::LayerEvictionTileIterator::operator*() const {
+  DCHECK(*this);
+  return *iterators_[iterator_index_];
+}
+
 PictureLayerImpl::LayerEvictionTileIterator&
 PictureLayerImpl::LayerEvictionTileIterator::
 operator++() {

cc/layers/picture_layer_impl.h

@@ -34,6 +34,7 @@ class CC_EXPORT PictureLayerImpl
     ~LayerRasterTileIterator();
 
     Tile* operator*();
+    const Tile* operator*() const;
     LayerRasterTileIterator& operator++();
     operator bool() const;
 
@@ -62,6 +63,7 @@ class CC_EXPORT PictureLayerImpl
     ~LayerEvictionTileIterator();
 
     Tile* operator*();
+    const Tile* operator*() const;
     LayerEvictionTileIterator& operator++();
     operator bool() const;