Fix missing const-reference on function parameter.

chrome/browser/ui/find_bar/find_bar_host_browsertest.cc

 // 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.
 
 #include "base/file_util.h"
 #include "base/message_loop/message_loop.h"
 #include "base/strings/string16.h"
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "chrome/app/chrome_command_ids.h"
@@ skipping 151 matching lines @@
       EXPECT_TRUE(GetFindBarWindowInfo(&position, &fully_visible));
       EXPECT_TRUE(fully_visible);
 
       // If the Find box has moved then we are done.
       if (position.x() != start_x_position)
         return position.x();
     }
     return start_x_position;
   }
 
-  GURL GetURL(const std::string filename) {
+  GURL GetURL(const std::string& filename) {
     return ui_test_utils::GetTestUrl(
         base::FilePath().AppendASCII("find_in_page"),
         base::FilePath().AppendASCII(filename));
   }
 
   void FlushHistoryService() {
     HistoryServiceFactory::GetForProfile(
         browser()->profile(), Profile::IMPLICIT_ACCESS)->FlushForTest(
         base::Bind(&base::MessageLoop::Quit,
                    base::Unretained(base::MessageLoop::current()->current())));
@@ skipping 1411 matching lines @@
 
   EXPECT_TRUE(chrome::ExecuteCommand(browser_incognito, IDC_FIND_NEXT));
   WebContents* web_contents_incognito =
       browser_incognito->tab_strip_model()->GetActiveWebContents();
   ui_test_utils::FindInPageNotificationObserver observer(
       web_contents_incognito);
   observer.Wait();
   EXPECT_EQ(ASCIIToUTF16("bar"),
             GetFindBarTextForBrowser(browser_incognito));
 }