chore(button): use disabled property, not attr (#1782)

src/lib/button/button.spec.ts

@@ -80,6 +80,16 @@ describe('MdButton', () => {
       expect(testComponent.clickCount).toBe(0);
     });
 
+    it('should disable the native button element', () => {
+      let fixture = TestBed.createComponent(TestApp);
+      let buttonNativeElement = fixture.nativeElement.querySelector('button');
+      expect(buttonNativeElement.disabled).toBeFalsy('Expected button not to be disabled');
+
+      fixture.componentInstance.isDisabled = true;
+      fixture.detectChanges();
+      expect(buttonNativeElement.disabled).toBeTruthy('Expected button to be disabled');
+    });
+
   });
 
   // Anchor button tests

src/lib/button/button.ts

@@ -21,7 +21,7 @@ import {MdRippleModule, coerceBooleanProperty} from '../core';
   selector: 'button[md-button], button[md-raised-button], button[md-icon-button], ' +
             'button[md-fab], button[md-mini-fab]',
   host: {
-    '[attr.disabled]': 'disabled',
+    '[disabled]': 'disabled',
     '[class.md-button-focus]': '_isKeyboardFocused',
     '(mousedown)': '_setMousedown()',
     '(focus)': '_setKeyboardFocus()',