Remove the ability of webpages to specify strings for the onbeforeunload dialog.

content/browser/web_contents/web_contents_impl_unittest.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 <stdint.h>
 #include <utility>
 
 #include "base/command_line.h"
 #include "base/logging.h"
 #include "base/macros.h"
@@ skipping 3390 matching lines @@
                            const std::string& accept_lang,
                            JavaScriptMessageType javascript_message_type,
                            const base::string16& message_text,
                            const base::string16& default_prompt_text,
                            const DialogClosedCallback& callback,
                            bool* did_suppress_message) override {
     *did_suppress_message = true;
   };
 
   void RunBeforeUnloadDialog(WebContents* web_contents,
-                             const base::string16& message_text,
                              bool is_reload,
                              const DialogClosedCallback& callback) override {}
 
   bool HandleJavaScriptDialog(WebContents* web_contents,
                               bool accept,
                               const base::string16* prompt_override) override {
     return true;
   }
 
   void CancelActiveAndPendingDialogs(WebContents* web_contents) override {}
@@ skipping 20 matching lines @@
   // An automatic navigation.
   contents()->GetMainFrame()->SendNavigateWithModificationCallback(
       2, 0, true, GURL(url::kAboutBlankURL), base::Bind(SetAsNonUserGesture));
 
   EXPECT_EQ(1u, delegate->reset_count());
 
   contents()->SetJavaScriptDialogManagerForTesting(nullptr);
 }
 
 }  // namespace content