feat(chip): add aria-selected to chip (#5920)

Author: tinayuangao

src/lib/chips/chip.spec.ts

@@ -164,6 +164,15 @@ describe('Chips', () => {
           expect(testComponent.chipDeselect).toHaveBeenCalledTimes(1);
           expect(testComponent.chipDeselect).toHaveBeenCalledWith(CHIP_EVENT);
         });
+
+        it('should have correct aria-selected', () => {
+          expect(chipNativeElement.getAttribute('aria-selected')).toBe('false');
+
+          testComponent.selected = true;
+          fixture.detectChanges();
+
+          expect(chipNativeElement.getAttribute('aria-selected')).toBe('true');
+        });
       });
 
       describe('when selectable is false', () => {
@@ -184,6 +193,15 @@ describe('Chips', () => {
           expect(chipInstance.selected).toBeFalsy();
           expect(testComponent.chipSelect).not.toHaveBeenCalled();
         });
+
+        it('should have empty aria-selected', () => {
+          expect(chipNativeElement.getAttribute('aria-selected')).toBeFalsy();
+
+          testComponent.selectable = true;
+          fixture.detectChanges();
+
+          expect(chipNativeElement.getAttribute('aria-selected')).toBe('false');
+        });
       });
 
       describe('when removable is true', () => {

src/lib/chips/chip.ts

@@ -60,6 +60,7 @@ export class MdBasicChip { }
     '[class.mat-chip-selected]': 'selected',
     '[attr.disabled]': 'disabled || null',
     '[attr.aria-disabled]': 'disabled.toString()',
+    '[attr.aria-selected]': 'ariaSelected',
     '(click)': '_handleClick($event)',
     '(keydown)': '_handleKeydown($event)',
     '(focus)': '_hasFocus = true',
@@ -118,6 +119,10 @@ export class MdChip extends _MdChipMixinBase implements Focusable, OnDestroy, Ca
   /** Emitted when the chip is destroyed. */
   @Output() destroy = new EventEmitter<MdChipEvent>();
 
+  get ariaSelected(): string {
+    return this.selectable ? this.selected.toString() : '';
+  }
+
   constructor(renderer: Renderer2, elementRef: ElementRef) {
     super(renderer, elementRef);
   }