Take testLaunchAndTappingCell test for example: (code is attached below)

This test fails when trying to tap "Tab 0_button" because it is still not accessible, and the reason is that showcase_utils::Open(@"TabGridViewController") introduces animations and apparently EarlGrey has some synchronization issues.

// Tests launching TabGridViewController and tapping a cell.
- (void)testLaunchAndTappingCell {
  showcase_utils::Open(@"TabGridViewController");
  [[EarlGrey selectElementWithMatcher:grey_accessibilityID(@"Tab 0_button")]
      performAction:grey_tap()];
  [[EarlGrey selectElementWithMatcher:grey_text(@"TabGridCommands")]
      assertWithMatcher:grey_notNil()];
  [[EarlGrey selectElementWithMatcher:grey_accessibilityLabel(
                                          @"protocol_alerter_done")]
      performAction:grey_tap()];
  showcase_utils::Close();
}

Ed and I tried to add a wait condition after showcase_utils::Open(@"TabGridViewController"); to wait for the target view (tab grid view) to become accessible, however, this still doesn't work because TabGridView becomes accessible doesn't necessarily mean that "Tab 0_button" is also accessible.

This flake applies to almost all showcase egtests, so we need a reliable solution to this issue so that future written tests can be flake-free.