cc: Fix invalidation problems in impl-side painting

cc/picture_layer_tiling_set.cc

Index: cc/picture_layer_tiling_set.cc
diff --git a/cc/picture_layer_tiling_set.cc b/cc/picture_layer_tiling_set.cc
index 4ec2e70b1d879f7d68b1a5e39fbf7dc4297837cb..7f5dcc90849ff8f118129c3e73f29fa8149ee94d 100644
--- a/cc/picture_layer_tiling_set.cc
+++ b/cc/picture_layer_tiling_set.cc
@@ -112,7 +112,7 @@ PictureLayerTilingSet::Iterator& PictureLayerTilingSet::Iterator::operator++() {
 
   // Loop until we find a valid place to stop.
   while (true) {
-    while (tiling_iter_ && !tiling_iter_->GetResourceId()) {
+    while (tiling_iter_ && (!*tiling_iter_ || !tiling_iter_->GetResourceId())) {
       missing_region_.Union(tiling_iter_.geometry_rect());
       ++tiling_iter_;
     }