Move another test to the UI thread.

Bug 27747569

A flaky error found caused durring verifyAssistDataNullness. The
method call has been moved to the UI thread in hopes that the
screen capture broadcast will have been received before the
value is checked on the UI thread, making this less flaky.

Change-Id: I7c9202a68486036871b66bb2c202f835a11f3a62
1 file changed