fix(chips): programmatically selected chip stealing focus (#7978)

Currently chips that are selected programmatically (e.g. by setting the of `ngModel`) will moves focus to themselves, causing the page the scroll down. This can be observed in the demo app where the bottom chip instances have a preselected value which shifts focus to the bottom. These changes fix the issue by only moving focus if the selection was a result of a user interaction.

Author: crisbeto

src/lib/chips/chip-list.spec.ts

@@ -577,6 +577,17 @@ describe('MatChipList', () => {
         expect(falsyFixture.componentInstance.chips.first.selected)
           .toBe(true, 'Expected first option to be selected');
       });
+
+      it('should not focus the active chip when the value is set programmatically', () => {
+        const chipArray = fixture.componentInstance.chips.toArray();
+
+        spyOn(chipArray[4], 'focus').and.callThrough();
+
+        fixture.componentInstance.control.setValue('chips-4');
+        fixture.detectChanges();
+
+        expect(chipArray[4].focus).not.toHaveBeenCalled();
+      });
     });
 
     describe('multiple selection', () => {

src/lib/chips/chip-list.ts

@@ -527,7 +527,6 @@ export class MatChipList implements MatFormFieldControl<any>, ControlValueAccess
   private _isInputEmpty(element: HTMLElement): boolean {
     if (element && element.nodeName.toLowerCase() === 'input') {
       let input = element as HTMLInputElement;
-
       return !input.value;
     }
 
@@ -547,7 +546,14 @@ export class MatChipList implements MatFormFieldControl<any>, ControlValueAccess
       // Shift focus to the active item. Note that we shouldn't do this in multiple
       // mode, because we don't know what chip the user interacted with last.
       if (correspondingChip) {
-        this._keyManager.setActiveItem(this.chips.toArray().indexOf(correspondingChip));
+        const correspondingChipIndex = this.chips.toArray().indexOf(correspondingChip);
+
+        if (isUserInput) {
+          this._keyManager.setActiveItem(correspondingChipIndex);
+        } else {
+          this._keyManager.updateActiveItemIndex(correspondingChipIndex);
+        }
+
       }
     }
   }