cc: Fix size_t to int truncations in tiles/ and trees/

cc/layers/layer_impl.h

Index: cc/layers/layer_impl.h
diff --git a/cc/layers/layer_impl.h b/cc/layers/layer_impl.h
index 980390224342fbe7b1dc03de3aa5a53ff557f4ff..7086841fcbb73529a8d46d1250a3d99623831dd0 100644
--- a/cc/layers/layer_impl.h
+++ b/cc/layers/layer_impl.h
@@ -807,7 +807,7 @@ class CC_EXPORT LayerImpl : public LayerAnimationValueObserver,
   // The number of direct children or dependent layers that need to be recursed
   // to in order for them or a descendent of them to push properties to the
   // active side.
-  int num_dependents_need_push_properties_;
+  size_t num_dependents_need_push_properties_;
 
   // Layers that share a sorting context id will be sorted together in 3d
   // space.  0 is a special value that means this layer will not be sorted and