Coverity: Fix several pass-by-values.

chrome/browser/themes/browser_theme_pack.h

Index: chrome/browser/themes/browser_theme_pack.h
diff --git a/chrome/browser/themes/browser_theme_pack.h b/chrome/browser/themes/browser_theme_pack.h
index 512103450d06a9b5791ec85d77aaeb8b547b9311..6091df57fca981d2bd5cec2b8962d5b647763631 100644
--- a/chrome/browser/themes/browser_theme_pack.h
+++ b/chrome/browser/themes/browser_theme_pack.h
@@ -65,7 +65,7 @@ class BrowserThemePack : public base::RefCountedThreadSafe<
   // operation should be relatively fast, as it should be an mmap() and some
   // pointer swizzling. Returns NULL on any error attempting to read |path|.
   static scoped_refptr<BrowserThemePack> BuildFromDataPack(
-      FilePath path, const std::string& expected_id);
+      const FilePath& path, const std::string& expected_id);
 
   // Builds a data pack on disk at |path| for future quick loading by
   // BuildFromDataPack(). Often (but not always) called from the file thread;