fix(autocomplete): remove aria-owns attribute while closed (#12333)

Removes the `aria-owns` attribute from the autocomplete trigger while the panel is closed.

Fixes #12332.

Author: crisbeto

src/lib/autocomplete/autocomplete-trigger.ts

@@ -103,7 +103,7 @@ export function getMatAutocompleteMissingPanelError(): Error {
     '[attr.aria-autocomplete]': 'autocompleteDisabled ? null : "list"',
     '[attr.aria-activedescendant]': 'activeOption?.id',
     '[attr.aria-expanded]': 'autocompleteDisabled ? null : panelOpen.toString()',
-    '[attr.aria-owns]': 'autocompleteDisabled ? null : autocomplete?.id',
+    '[attr.aria-owns]': '(autocompleteDisabled || !panelOpen) ? null : autocomplete?.id',
     // Note: we use `focusin`, as opposed to `focus`, in order to open the panel
     // a little earlier. This avoids issues where IE delays the focusing of the input.
     '(focusin)': '_handleFocus()',

src/lib/autocomplete/autocomplete.spec.ts

@@ -1329,7 +1329,16 @@ describe('MatAutocomplete', () => {
       const panel = fixture.debugElement.query(By.css('.mat-autocomplete-panel')).nativeElement;
 
       expect(input.getAttribute('aria-owns'))
-          .toEqual(panel.getAttribute('id'), 'Expected aria-owns to match attached autocomplete.');
+          .toBe(panel.getAttribute('id'), 'Expected aria-owns to match attached autocomplete.');
+    });
+
+    it('should not set aria-owns while the autocomplete is closed', () => {
+      expect(input.getAttribute('aria-owns')).toBeFalsy();
+
+      fixture.componentInstance.trigger.openPanel();
+      fixture.detectChanges();
+
+      expect(input.getAttribute('aria-owns')).toBeTruthy();
     });
 
     it('should restore focus to the input when clicking to select a value', fakeAsync(() => {