Coverity: Fix several pass-by-values.

chrome/browser/themes/browser_theme_pack.h

 // Copyright (c) 2012 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.
 
 #ifndef CHROME_BROWSER_THEMES_BROWSER_THEME_PACK_H_
 #define CHROME_BROWSER_THEMES_BROWSER_THEME_PACK_H_
 
 #include <map>
 #include <string>
 
@@ skipping 47 matching lines @@
   // Builds the theme pack from all data from |extension|. This is often done
   // on a separate thread as it takes so long. This can fail and return NULL in
   // the case where the theme has invalid data.
   static scoped_refptr<BrowserThemePack> BuildFromExtension(
       const extensions::Extension* extension);
 
   // Builds the theme pack from a previously performed WriteToDisk(). This
   // 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;
   // implementation should be threadsafe because neither thread will write to
   // |image_memory_| and the worker thread will keep a reference to prevent
   // destruction.
   bool WriteToDisk(const FilePath& path) const;
 
   // If this theme specifies data for the corresponding |id|, return true and
   // write the corresponding value to the output parameter. These functions
@@ skipping 163 matching lines @@
   // in |image_memory_| that are in |prepared_images_| or vice versa.
   ImageCache prepared_images_;
 
   // Loaded images. These are loaded from |image_memory_| or the |data_pack_|.
   mutable ImageCache loaded_images_;
 
   DISALLOW_COPY_AND_ASSIGN(BrowserThemePack);
 };
 
 #endif  // CHROME_BROWSER_THEMES_BROWSER_THEME_PACK_H_