Fixed issue which caused AssistantOptInView to be painted wrong.

I was unable to repro the bug consistently with an unaltered build.
I was able to repro the bug, however, with some local changes in which
I posted the UpdateLabel calls to simulate a timing issue. With this
change, I was able to reproduce the bug consistently.

Bug: b:130758812
Change-Id: I063527e9c52f5584104ce556d3558fc4ed62e228
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1577494
Reviewed-by: Tao Wu <wutao@chromium.org>
Commit-Queue: David Black <dmblack@google.com>
Cr-Commit-Position: refs/heads/master@{#652883}
1 file changed