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

cc/tiles/picture_layer_tiling_set.h

Index: cc/tiles/picture_layer_tiling_set.h
diff --git a/cc/tiles/picture_layer_tiling_set.h b/cc/tiles/picture_layer_tiling_set.h
index 7e54411cd1ac71fafe3b87bb657e18b9241fcaca..dd84ca0496097aa22b5453da98b2d1573a63396a 100644
--- a/cc/tiles/picture_layer_tiling_set.h
+++ b/cc/tiles/picture_layer_tiling_set.h
@@ -152,14 +152,14 @@ class CC_EXPORT PictureLayerTilingSet {
     PictureLayerTiling* CurrentTiling() const;
 
    private:
-    int NextTiling() const;
+    size_t NextTiling() const;
 
     const PictureLayerTilingSet* set_;
     float contents_scale_;
     float ideal_contents_scale_;
     PictureLayerTiling::CoverageIterator tiling_iter_;
-    int current_tiling_;
-    int ideal_tiling_;
+    size_t current_tiling_;
+    size_t ideal_tiling_;
 
     Region current_region_;
     Region missing_region_;