[presubmit] Enable runtime/threadsafe_fn linter checking.

[presubmit] Enable runtime/threadsafe_fn linter checking.

This enables linter checking for "runtime/threadsafe_fn" violations
during presubmit and instead marks the few known exceptions that we
allow explicitly.

R=jochen@chromium.org

Committed: https://crrev.com/6ec34c7cb3fc8f9d8fdde7e3e673da15b7ce7912
Cr-Commit-Position: refs/heads/master@{#30933}

[jochen (gone - plz use gerrit), 2015-09-25 11:20:41]

lgtm

[Michael Starzinger, 2015-09-25 11:25:46]

The CQ bit was checked by mstarzinger@chromium.org

[commit-bot: I haz the power, 2015-09-25 11:26:00]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1369673003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1369673003/1

[commit-bot: I haz the power, 2015-09-25 11:32:42]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-25 11:32:59]

Patchset 1 (id:??) landed as
https://crrev.com/6ec34c7cb3fc8f9d8fdde7e3e673da15b7ce7912
Cr-Commit-Position: refs/heads/master@{#30933}