webui: rename "DialogClose" to "dialogClose" to match other webui messages.

chrome/browser/resources/chromeos/keyboard_overlay.js

 // 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 src="keyboard_overlay_data.js"/>
 <include src="keyboard_overlay_accessibility_helper.js"/>
 
 var BASE_KEYBOARD = {
   top: 0,
   left: 0,
@@ skipping 698 matching lines @@
     chrome.send('didPaint');
   });
 }
 
 /**
  * Handles click events of the learn more link.
  * @param {Event} e Mouse click event.
  */
 function learnMoreClicked(e) {
   chrome.send('openLearnMorePage');
-  chrome.send('DialogClose');
+  chrome.send('dialogClose');
   e.preventDefault();
 }
 
 document.addEventListener('DOMContentLoaded', init);