fix(bottom-sheet): don't move focus if it was moved during close animation

src/material/bottom-sheet/bottom-sheet-container.ts

@@ -222,7 +222,17 @@ export class MatBottomSheetContainer extends BasePortalOutlet implements OnDestr
 
     // We need the extra check, because IE can set the `activeElement` to null in some cases.
     if (this.bottomSheetConfig.restoreFocus && toFocus && typeof toFocus.focus === 'function') {
-      toFocus.focus();
+      const activeElement = this._document.activeElement;
+      const element = this._elementRef.nativeElement;
+
+      // Make sure that focus is still inside the bottom sheet or is on the body (usually because a
+      // non-focusable element like the backdrop was clicked) before moving it. It's possible that
+      // the consumer moved it themselves before the animation was done, in which case we shouldn't
+      // do anything.
+      if (!activeElement || activeElement === this._document.body || activeElement === element ||
+        element.contains(activeElement)) {
+        toFocus.focus();
+      }
     }
 
     if (this._focusTrap) {

src/material/bottom-sheet/bottom-sheet.spec.ts

@@ -690,6 +690,44 @@ describe('MatBottomSheet', () => {
       document.body.removeChild(button);
     }));
 
+    it('should not move focus if it was moved outside the sheet while animating', fakeAsync(() => {
+      // Create a element that has focus before the bottom sheet is opened.
+      const button = document.createElement('button');
+      const otherButton = document.createElement('button');
+      const body = document.body;
+      button.id = 'bottom-sheet-trigger';
+      otherButton.id = 'other-button';
+      body.appendChild(button);
+      body.appendChild(otherButton);
+      button.focus();
+
+      const bottomSheetRef = bottomSheet.open(PizzaMsg, {viewContainerRef: testViewContainerRef});
+
+      flushMicrotasks();
+      viewContainerFixture.detectChanges();
+      flushMicrotasks();
+
+      expect(document.activeElement!.id).not.toBe('bottom-sheet-trigger',
+          'Expected the focus to change when the bottom sheet was opened.');
+
+      // Start the closing sequence and move focus out of bottom sheet.
+      bottomSheetRef.dismiss();
+      otherButton.focus();
+
+      expect(document.activeElement!.id)
+          .toBe('other-button', 'Expected focus to be on the alternate button.');
+
+      flushMicrotasks();
+      viewContainerFixture.detectChanges();
+      flush();
+
+      expect(document.activeElement!.id)
+          .toBe('other-button', 'Expected focus to stay on the alternate button.');
+
+      body.removeChild(button);
+      body.removeChild(otherButton);
+    }));
+
   });
 
 });