Avoid crash when ServiceTabLauncher::OnTabLaunched given bad request_id

The |request_id| given to OnTabLaunched should be in the
tab_launched_callbacks_ set, however it is not always the case. Don't
crash.

R=tedchoc@chromium.org

Bug: 962873
Change-Id: Iaea08c2ff2a41527dacce84e84afa396c04efc65
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1613673
Reviewed-by: Ted Choc <tedchoc@chromium.org>
Commit-Queue: danakj <danakj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#660179}
1 file changed