Clarify comment in SingleThreadTaskRunner.java

Bug: 863341, 872372
Change-Id: I19405b9061b3dc677d1f06e16564eb9aed133f79
Reviewed-on: https://chromium-review.googlesource.com/1251546
Commit-Queue: Gabriel Charette <gab@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595569}
1 file changed