fix(menu): ensure menu button is type=button

closes #3821

Author: rschmukler

src/components/menu/_menu.js

@@ -151,6 +151,7 @@ function MenuDirective($mdMenu) {
       triggerElement = triggerElement.querySelector('[ng-click]');
     }
     triggerElement && triggerElement.setAttribute('aria-haspopup', 'true');
+    triggerElement.setAttribute('type', 'button');
     if (templateElement.children().length != 2) {
       throw Error('Invalid HTML for md-menu. Expected two children elements.');
     }

src/components/menu/menu.spec.js

@@ -23,12 +23,18 @@ describe('md-menu directive', function () {
     expect(buildBadMenu).toThrow();
   }));
 
+
   it('removes everything but the first element', function () {
     var menu = setup()[0];
     expect(menu.children.length).toBe(1);
     expect(menu.firstElementChild.nodeName).toBe('BUTTON');
   });
 
+  iit('specifies button type', inject(function($compile, $rootScope) {
+    var menu = setup()[0];
+    expect(menu.firstElementChild.getAttribute('type')).toBe('button');
+  }));
+
   it('opens on click', function () {
     var menu = setup();
     openMenu(menu);