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

content/browser/frame_host/render_frame_host_impl.cc

 // Copyright 2013 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 "content/browser/frame_host/render_frame_host_impl.h"
 
 #include <utility>
 
 #include "base/bind.h"
 #include "base/command_line.h"
@@ skipping 1423 matching lines @@
   // While a JS message dialog is showing, tabs in the same process shouldn't
   // process input events.
   GetProcess()->SetIgnoreInputEvents(true);
   render_view_host_->GetWidget()->StopHangMonitorTimeout();
   delegate_->RunJavaScriptMessage(this, message, default_prompt,
                                   frame_url, type, reply_msg);
 }
 
 void RenderFrameHostImpl::OnRunBeforeUnloadConfirm(
     const GURL& frame_url,
-    const base::string16& message,
     bool is_reload,
     IPC::Message* reply_msg) {
   // While a JS beforeunload dialog is showing, tabs in the same process
   // shouldn't process input events.
   GetProcess()->SetIgnoreInputEvents(true);
   render_view_host_->GetWidget()->StopHangMonitorTimeout();
-  delegate_->RunBeforeUnloadConfirm(this, message, is_reload, reply_msg);
+  delegate_->RunBeforeUnloadConfirm(this, is_reload, reply_msg);
 }
 
 void RenderFrameHostImpl::OnTextSurroundingSelectionResponse(
     const base::string16& content,
     uint32_t start_offset,
     uint32_t end_offset) {
   render_view_host_->OnTextSurroundingSelectionResponse(
       content, start_offset, end_offset);
 }
 
@@ skipping 1251 matching lines @@
   FrameTreeNode* focused_frame_tree_node = frame_tree_->GetFocusedFrame();
   if (!focused_frame_tree_node)
     return;
   RenderFrameHostImpl* focused_frame =
       focused_frame_tree_node->current_frame_host();
   DCHECK(focused_frame);
   dst->focused_tree_id = focused_frame->GetAXTreeID();
 }
 
 }  // namespace content