refactor(button): use [attr.disabled] host binding in MatButton (#15308)

Author: jelbourn

src/lib/button/button.spec.ts

@@ -43,8 +43,9 @@ describe('MatButton', () => {
 
   it('should expose the ripple instance', () => {
     const fixture = TestBed.createComponent(TestApp);
-    const button = fixture.debugElement.query(By.css('button')).componentInstance as MatButton;
+    fixture.detectChanges();
 
+    const button = fixture.debugElement.query(By.directive(MatButton)).componentInstance;
     expect(button.ripple).toBeTruthy();
   });
 

src/lib/button/button.ts

@@ -70,7 +70,7 @@ export const _MatButtonMixinBase:
              button[mat-flat-button]`,
   exportAs: 'matButton',
   host: {
-    '[disabled]': 'disabled || null',
+    '[attr.disabled]': 'disabled || null',
     '[class._mat-animation-noopable]': '_animationMode === "NoopAnimations"',
   },
   templateUrl: 'button.html',