Instant interactive_ui_tests should wait for main frame load.
Before this patch, instant search tests didn't wait for the main frame load before executing javascript, resulting in running javascript in incomplete document.
blink: https://codereview.chromium.org/263583002/
It seems that the valid document were luckily there when we run these tests before the blink CL, but the blink CL changes the timeline so it fails on these tests.
BUG=368548, 368555
Review URL: https://codereview.chromium.org/
302433013
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@273996 0039d316-1c4b-4281-b951-d872f2087c98