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

cc/trees/layer_tree_impl.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/trees/layer_tree_impl.h"
 
 #include <algorithm>
 #include <limits>
 #include <set>
 
@@ skipping 1343 matching lines @@
   // closer in this case, counterintuitively.
   float closest_distance;
 };
 
 template <typename Functor>
 static void FindClosestMatchingLayer(
     const gfx::PointF& screen_space_point,
     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;
   if (func(layer) &&
       PointHitsLayer(layer, screen_space_point, &distance_to_intersection) &&
       ((!data_for_recursion->closest_match ||
         distance_to_intersection > data_for_recursion->closest_distance))) {
     data_for_recursion->closest_distance = distance_to_intersection;
     data_for_recursion->closest_match = layer;
   }
@@ skipping 212 matching lines @@
     scoped_ptr<PendingPageScaleAnimation> pending_animation) {
   pending_page_scale_animation_ = pending_animation.Pass();
 }
 
 scoped_ptr<PendingPageScaleAnimation>
     LayerTreeImpl::TakePendingPageScaleAnimation() {
   return pending_page_scale_animation_.Pass();
 }
 
 }  // namespace cc