A number of EG tests used to have code that did the following:

  chrome_test_util::CloseAllTabsInCurrentMode();
  chrome_test_util::OpenNewTab();

Closing all tabs triggered the tabs switcher animation, but then OpenNewTab() was called before the animation could complete.  In practice, this ended up running both switcher animations concurrently, which is a weird state to be in.

Switching to BVC presentation broke this code entirely, because the VC dismissal hasn't even taken effect yet when OpenNewTab() is called.  This was resolved by adding a delayUntilIdle after closing all tabs.

The VC presentation/dismissal here should be reworked so that it becomes possible to interrupt/reverse an existing or pending transition.