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

cc/trees/layer_tree_impl.cc

Index: cc/trees/layer_tree_impl.cc
diff --git a/cc/trees/layer_tree_impl.cc b/cc/trees/layer_tree_impl.cc
index c44eecc1113d7bcae48a11c154f10ca2c8039ac0..3e7821aa7c3d1958e48bfa20037205afcf64908f 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -1361,9 +1361,11 @@ static void FindClosestMatchingLayer(
     LayerImpl* layer,
     const Functor& func,
     FindClosestMatchingLayerDataForRecursion* data_for_recursion) {
-  for (int i = layer->children().size() - 1; i >= 0; --i) {
-    FindClosestMatchingLayer(
-        screen_space_point, layer->children()[i], func, data_for_recursion);
+  size_t children_size = layer->children().size();
+  for (size_t i = 0; i < children_size; ++i) {
+    size_t index = children_size - 1 - i;
+    FindClosestMatchingLayer(screen_space_point, layer->children()[index], func,
+                             data_for_recursion);
   }
 
   float distance_to_intersection = 0.f;