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

components/test_runner/web_frame_test_proxy.h

 // 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.
 
 #ifndef COMPONENTS_TEST_RUNNER_WEB_FRAME_TEST_PROXY_H_
 #define COMPONENTS_TEST_RUNNER_WEB_FRAME_TEST_PROXY_H_
 
 #include "base/macros.h"
 #include "components/test_runner/mock_screen_orientation_client.h"
 #include "components/test_runner/web_test_delegate.h"
@@ skipping 149 matching lines @@
 
   bool runModalPromptDialog(const blink::WebString& message,
                             const blink::WebString& default_value,
                             blink::WebString*) override {
     base_proxy_->GetDelegate()->PrintMessage(
         std::string("PROMPT: ") + message.utf8().data() + ", default text: " +
         default_value.utf8().data() + "\n");
     return true;
   }
 
-  bool runModalBeforeUnloadDialog(bool is_reload,
-                                  const blink::WebString& message) override {
+  bool runModalBeforeUnloadDialog(bool is_reload) override {
     base_proxy_->GetDelegate()->PrintMessage(
-        std::string("CONFIRM NAVIGATION: ") + message.utf8().data() + "\n");
+        std::string("CONFIRM NAVIGATION\n"));
     return !base_proxy_->GetInterfaces()
                 ->TestRunner()
                 ->ShouldStayOnPageAfterHandlingBeforeUnload();
   }
 
   void showContextMenu(
       const blink::WebContextMenuData& context_menu_data) override {
     base_proxy_->ShowContextMenu(context_menu_data);
     Base::showContextMenu(context_menu_data);
   }
@@ skipping 97 matching lines @@
 
  private:
   WebTestProxyBase* base_proxy_;
 
   DISALLOW_COPY_AND_ASSIGN(WebFrameTestProxy);
 };
 
 }  // namespace test_runner
 
 #endif  // COMPONENTS_TEST_RUNNER_WEB_FRAME_TEST_PROXY_H_