Cleanup: Pass std::string as const reference if possible

chrome/browser/dom_distiller/dom_distiller_viewer_source_browsertest.cc

 // Copyright 2014 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 <string.h>
 
 #include "base/command_line.h"
 #include "base/guid.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/strings/utf_string_conversions.h"
@@ skipping 53 matching lines @@
 const char kGetBodyClass[] =
     "window.domAutomationController.send("
         "document.body.className)";
 
 const unsigned kDarkToolbarThemeColor = 0xFF1A1A1A;
 
 void AddEntry(const ArticleEntry& e, FakeDB<ArticleEntry>::EntryMap* map) {
   (*map)[e.entry_id()] = e;
 }
 
-ArticleEntry CreateEntry(std::string entry_id, std::string page_url) {
+ArticleEntry CreateEntry(const std::string& entry_id,
+                         const std::string& page_url) {
   ArticleEntry entry;
   entry.set_entry_id(entry_id);
   if (!page_url.empty()) {
     ArticleEntryPage* page = entry.add_pages();
     page->set_url(page_url);
   }
   return entry;
 }
 
 }  // namespace
@@ skipping 360 matching lines @@
   EXPECT_EQ(kDarkToolbarThemeColor, contents->GetThemeColor());
 
   distilled_page_prefs->SetFontFamily(DistilledPagePrefs::SERIF);
   base::RunLoop().RunUntilIdle();
   EXPECT_TRUE(
       content::ExecuteScriptAndExtractString(contents, kGetBodyClass, &result));
   EXPECT_EQ("dark serif", result);
 }
 
 }  // namespace dom_distiller