Similar to Firefox and Safari, calling console.time() repeatedly with
the same label will now produce a console warning indicating that the
label already exists.  Similarly for console.timeEnd() as well.

Bug: chromium:727514
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Id644ee107b09e7f4686fff44c5f32d31c88371ad
Reviewed-on: https://chromium-review.googlesource.com/794345
Commit-Queue: Erik Luo <luoe@chromium.org>
Reviewed-by: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49803}