[DevTools] Don't handle shortcuts while dialog is open.

Source/devtools/front_end/Dialog.js

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 41 matching lines @@
         WebInspector.KeyboardShortcut.Keys.Esc.code,
     ];
 
     delegate.show(this._element);
 
     this._position();
     this._delegate.focus();
 }
 
 /**
- * @return {!WebInspector.Dialog}
+ * @return {?WebInspector.Dialog}
  */
 WebInspector.Dialog.currentInstance = function()
 {
     return WebInspector.Dialog._instance;
 }
 
 /**
  * @param {!Element} relativeToElement
  * @param {!WebInspector.DialogDelegate} delegate
  */
@@ skipping 125 matching lines @@
 {
     return WebInspector.Dialog._modalHostView;
 };
 
 WebInspector.Dialog.modalHostRepositioned = function()
 {
     if (WebInspector.Dialog._instance)
         WebInspector.Dialog._instance._position();
 };