Anti-shelf-overlapping fixes for several menus.

ui/login/login_ui_tools.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 JS helpers used on login.
+ */
+
+cr.define('cr.ui.LoginUITools', function() {
+  return {
+    /**
+     * Computes max-height for an element so that it doesn't overlap shelf.
+     * @param {element} DOM element
+     */
+    getMaxHeightBeforeShelfOverlapping : function(element) {
+      var maxAllowedHeight =
+          $('outer-container').offsetHeight -
+          element.getBoundingClientRect().top -
+          parseInt(window.getComputedStyle(element).marginTop) -
+          parseInt(window.getComputedStyle(element).marginBottom);
+      return maxAllowedHeight;
+    }
+  }
+});