Preparations for adding options and different render types to render_pictures.

Review URL: https://codereview.appspot.com/6345107

git-svn-id: http://skia.googlecode.com/svn/trunk@4603 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/tools/picture_utils.cpp b/tools/picture_utils.cpp
index 98351b8..28e6293 100644
--- a/tools/picture_utils.cpp
+++ b/tools/picture_utils.cpp
@@ -13,8 +13,8 @@
 
 namespace sk_tools {
 
-    void make_filepath(SkString* path, const char* dir, const SkString& name) {
-        size_t len = strlen(dir);
+    void make_filepath(SkString* path, const SkString& dir, const SkString& name) {
+        size_t len = dir.size();
         path->set(dir);
         if (0 < len  && '/' != dir[len - 1]) {
             path->append("/");