Fix opacity transition of pin keyboard on lockscreen.

ui/login/resource_loader.js

 // 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.
 
 /**
  * @fileoverview Deferred resource loader for OOBE/Login screens.
  */
 
 cr.define('cr.ui.login.ResourceLoader', function() {
   'use strict';
@@ skipping 190 matching lines @@
       }, { timeout: opt_idleTimeoutMs });
     };
 
     if (document.readyState == 'complete') {
       loadOnIdle();
     } else {
       window.addEventListener('DOMContentLoaded', loadOnIdle);
     }
   }
 
+  /**
+   * Wait until the element with the given |id| has finished its layout,
+   * specifically, after it has an offsetHeight > 0.
+   * @param {string} id Identifier of the element to wait for.
+   * @param {function()} callback Function to invoke when done loading.
+   */
+  function waitUntilLayoutComplete(id, callback) {
+    function doWait() {

[xiyuan, 2016/05/20 21:06:32]

nit: var doWait = function() {...};

[1]
https://google.github.io/styleguide/javascriptguide.xml?showone=Function_Decl...

[jdufault, 2016/05/20 21:31:06]

Done.

+      var element = $(id);
+      if (!element || !element.offsetHeight) {
+        setTimeout(doWait, 0);
+        return;
+      }
+
+      callback(element);
+    }
+
+    setTimeout(doWait, 0);

[xiyuan, 2016/05/20 21:06:32]

nit: Would window.requestAnimationFrame be better since it is called before the
next repaint?

[jdufault, 2016/05/20 21:31:06]

Makes sense. Done.

+  }
+
   return {
     alreadyLoadedAssets: alreadyLoadedAssets,
     hasDeferredAssets: hasDeferredAssets,
     loadAssets: loadAssets,
     loadAssetsOnIdle: loadAssetsOnIdle,
+    waitUntilLayoutComplete: waitUntilLayoutComplete,
     registerAssets: registerAssets
   };
 });