Close web contents modal dialogs on content load start

chrome/browser/ui/cocoa/constrained_window/constrained_window_mac.mm

 // 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 "chrome/browser/ui/cocoa/constrained_window/constrained_window_mac.h"
 
 #include "base/logging.h"
 #include "chrome/browser/ui/browser_finder.h"
 #include "chrome/browser/ui/browser_window.h"
 #import "chrome/browser/ui/cocoa/constrained_window/constrained_window_sheet.h"
@@ skipping 60 matching lines @@
       pulseSheet:sheet_];
 }
 
 NativeWebContentsModalDialog ConstrainedWindowMac::GetNativeDialog() {
   // TODO(wittman): Ultimately this should be changed to the
   // ConstrainedWindowSheet pointer, in conjunction with the corresponding
   // changes to NativeWebContentsModalDialogManagerCocoa.
   return this;
 }
 
+void ConstrainedWindowMac::SetPreventCloseOnLoadStart(bool prevent) {
+  WebContentsModalDialogManager* web_contents_modal_dialog_manager =
+      WebContentsModalDialogManager::FromWebContents(web_contents_);
+  web_contents_modal_dialog_manager->SetPreventCloseOnLoadStart(
+      GetNativeDialog(),
+      prevent);
+}
+
 NSWindow* ConstrainedWindowMac::GetParentWindow() const {
   // Tab contents in a tabbed browser may not be inside a window. For this
   // reason use a browser window if possible.
   Browser* browser = chrome::FindBrowserWithWebContents(web_contents_);
   if (browser)
     return browser->window()->GetNativeWindow();
 
   return web_contents_->GetView()->GetTopLevelNativeWindow();
 }