feat(menu): add support for md-autofocus attribute

* Currently, the most common components are supporting `md-autofocus`, except the `$mdMenu` component.
  `md-menu` did only support `md-menu-focus-target`, which was a unclear and undocumented attribute.

* This commit adds support for the `md-autofocus` directive, to be consistent with the whole API.
   It also adds a documentation for the focus behavior in `md-menu`.

Closes #7868.

Closes #8469

Author: devversion

src/components/menu/js/menuController.js

@@ -153,7 +153,7 @@ function MenuController($mdMenu, $attrs, $element, $scope, $mdUtil, $timeout, $r
   };
 
   this.focusMenuContainer = function focusMenuContainer() {
-    var focusTarget = menuContainer[0].querySelector('[md-menu-focus-target]');
+    var focusTarget = menuContainer[0].querySelector('[md-menu-focus-target], [md-autofocus]');
     if (!focusTarget) focusTarget = menuContainer[0].querySelector('.md-button');
     focusTarget.focus();
   };

src/components/menu/js/menuDirective.js

@@ -102,7 +102,22 @@
  *   <!-- menu-content -->
  * </md-menu>
  * </hljs>
-
+ *
+ * ### Auto Focus
+ * By default, when a menu opens, `md-menu` focuses the first button in the menu content.
+ * 
+ * But sometimes you would like to focus another specific menu item instead of the first.<br/>
+ * This can be done by applying the `md-autofocus` directive on the given element.
+ *
+ * <hljs lang="html">
+ * <md-menu-item>
+ *   <md-button md-autofocus ng-click="doSomething()">
+ *     Auto Focus
+ *   </md-button>
+ * </md-menu-item>
+ * </hljs>
+ *
+ *
  * ### Preventing close
  *
  * Sometimes you would like to be able to click on a menu item without having the menu

src/components/menu/js/menuServiceProvider.js

@@ -210,7 +210,7 @@ function MenuProvider($$interimElementProvider) {
         opts.menuContentEl[0].addEventListener('click', captureClickListener, true);
 
         // kick off initial focus in the menu on the first element
-        var focusTarget = opts.menuContentEl[0].querySelector('[md-menu-focus-target]');
+        var focusTarget = opts.menuContentEl[0].querySelector('[md-menu-focus-target], [md-autofocus]');
         if ( !focusTarget ) {
           var firstChild = opts.menuContentEl[0].firstElementChild;
 

src/components/menu/menu.spec.js

@@ -141,6 +141,48 @@ describe('material.components.menu', function() {
       expect(getOpenMenuContainer(menu).length).toBe(0);
     }));
 
+    describe('autofocus', function() {
+
+      it('should focus a button with md-menu-focus-target', inject(function($compile, $rootScope, $document) {
+        var menu = $compile(
+          '<md-menu>' +
+            '<button ng-click="$mdOpenMenu($event)">Hello World</button>' +
+            '<md-menu-content>' +
+              '<md-menu-item>' +
+                '<button id="menuFocus" md-menu-focus-target ng-click="doSomething($event)"></button>' +
+              '</md-menu-item>' +
+            '</md-menu-content>' +
+          '</md-menu>'
+        )($rootScope);
+
+        openMenu(menu);
+
+        var menuTarget = $document[0].querySelector('#menuFocus');
+
+        expect(document.activeElement).toBe(menuTarget);
+      }));
+
+      it('should focus a button with md-autofocus', inject(function($compile, $rootScope, $document) {
+        var menu = $compile(
+          '<md-menu>' +
+            '<button ng-click="$mdOpenMenu($event)">Hello World</button>' +
+            '<md-menu-content>' +
+              '<md-menu-item>' +
+                '<button id="menuFocus" md-autofocus ng-click="doSomething($event)"></button>' +
+              '</md-menu-item>' +
+            '</md-menu-content>' +
+          '</md-menu>'
+        )($rootScope);
+
+        openMenu(menu);
+
+        var menuTarget = $document[0].querySelector('#menuFocus');
+
+        expect(document.activeElement).toBe(menuTarget);
+      }));
+
+    });
+
     describe('closes with -', function() {
       it('closes on normal option click', function() {
 

src/core/util/autofocus.js

@@ -13,7 +13,7 @@ angular.module('material.core')
  * @description
  *
  * `[md-autofocus]` provides an optional way to identify the focused element when a `$mdDialog`,
- * `$mdBottomSheet`, or `$mdSidenav` opens or upon page load for input-like elements.
+ * `$mdBottomSheet`, `$mdMenu` or `$mdSidenav` opens or upon page load for input-like elements.
  *
  * When one of these opens, it will find the first nested element with the `[md-autofocus]`
  * attribute directive and optional expression. An expression may be specified as the directive