GitLab

The timer crashes if stopped is called before started. Add a null pointer
check to avoid that.

Also add a DCHECK for Reset() which should never be called before Start().

Bug: 956237
Change-Id: I76c0d3522c4aa0793a2375f3c1b94723c03db915
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1787701
Commit-Queue: Owen Min <zmin@chromium.org>
Reviewed-by: Julian Pastarmov <pastarmovj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#694314}