The RuntimeCallStats object happen to be created on the main thread,
but then got used in a worker. Make sure the thread checks do not
fire false positives in this case.

BUG=chromium:760649

Change-Id: I8f2a2b4d1da1bc48416987ea378688ec15b9d955
Reviewed-on: https://chromium-review.googlesource.com/706181Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Alexei Filippov <alph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48409}