fix(select): use parsed attribute for md-container-class attribute

Fixes #6973

  Closes #6976

Author: devversion

src/components/select/select.js

@@ -430,8 +430,8 @@ function SelectDirective($mdSelect, $mdUtil, $mdTheming, $mdAria, $compile, $par
           element[0].querySelector('.md-select-menu-container')
         );
         selectScope = scope;
-        if (element.attr('md-container-class')) {
-          var value = selectContainer[0].getAttribute('class') + ' ' + element.attr('md-container-class');
+        if (attr.mdContainerClass) {
+          var value = selectContainer[0].getAttribute('class') + ' ' + attr.mdContainerClass;
           selectContainer[0].setAttribute('class', value);
         }
         selectMenuCtrl = selectContainer.find('md-select-menu').controller('mdSelectMenu');

src/components/select/select.spec.js

@@ -57,6 +57,24 @@ describe('<md-select>', function() {
     expect(container.classList.contains('test')).toBe(true);
   }));
 
+  it('supports passing classes to the container using `data-` attribute prefix', inject(function($document) {
+    var select = setupSelect('ng-model="val", data-md-container-class="test"').find('md-select');
+    openSelect(select);
+
+    var container = $document[0].querySelector('.md-select-menu-container');
+    expect(container).toBeTruthy();
+    expect(container.classList.contains('test')).toBe(true);
+  }));
+
+  it('supports passing classes to the container using `x-` attribute prefix', inject(function($document) {
+    var select = setupSelect('ng-model="val", x-md-container-class="test"').find('md-select');
+    openSelect(select);
+
+    var container = $document[0].querySelector('.md-select-menu-container');
+    expect(container).toBeTruthy();
+    expect(container.classList.contains('test')).toBe(true);
+  }));
+
   it('sets aria-owns between the select and the container', function() {
     var select = setupSelect('ng-model="val"').find('md-select');
     var ownsId = select.attr('aria-owns');