[MD Extensions] Implement keyboard shortcuts page

chrome/test/data/webui/extensions/extension_keyboard_shortcuts_test.js

 // Copyright 2016 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 Suite of tests for extension-keyboard-shortcuts. */
 cr.define('extension_keyboard_shortcut_tests', function() {
   /** @enum {string} */
   var TestNames = {
     Layout: 'Layout',
     // The ShortcutUtil test suite is all js-based (no UI), so we can execute
@@ skipping 64 matching lines @@
         var cards =
             keyboardShortcuts.$$('#main').querySelectorAll('.shortcut-card');
         assertEquals(2, cards.length);
 
         var card1 = cards[0];
         expectEquals(oneCommand.name,
                      card1.querySelector('.card-title span').textContent);
         var commands = card1.querySelectorAll('.command-entry');
         assertEquals(1, commands.length);
         expectTrue(isVisibleOnCard(commands[0], '.command-name'));
-        expectTrue(isVisibleOnCard(commands[0], '.command-keys'));
-        expectFalse(isVisibleOnCard(commands[0], '.no-command-set'));
         expectTrue(isVisibleOnCard(commands[0], 'paper-dropdown-menu'));
 
         var card2 = cards[1];
         commands = card2.querySelectorAll('.command-entry');
         assertEquals(2, commands.length);
-        expectFalse(isVisibleOnCard(commands[1], '.command-keys'));
-        expectTrue(isVisibleOnCard(commands[1], '.no-command-set'));
 
         expectEquals(
             1,
             keyboardShortcuts.computeSelectedScope_(twoCommands.commands[0]));
         expectEquals(
             0,
             keyboardShortcuts.computeSelectedScope_(twoCommands.commands[1]));
       });
     });
     suite(assert(TestNames.ShortcutUtil), function() {
@@ skipping 24 matching lines @@
         expectEquals('Ctrl+Shift+A', extensions.keystrokeToString(e));
       });
     });
   }
 
   return {
     registerTests: registerTests,
     TestNames: TestNames,
   };
 });