[tab_under] Add console logging unit test

Now that RenderFrameHostTesters keep track of these messages, it makes
writing unit tests pretty easy.

Bug: 661629
Change-Id: I3ddd13d7d9a83a90dba70dc6807073bf3d4b2b46
Reviewed-on: https://chromium-review.googlesource.com/749319
Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Charlie Harrison <csharrison@chromium.org>
Cr-Commit-Position: refs/heads/master@{#513231}
1 file changed