Get rid of having users dispatch control runnables. It was error prone and
required too much reasoning. It was also possible to end up in a state where
callers would dispatch a WorkerRunnable, which would succeed, so they would not
dispatch a WorkerControlRunnable. Then the worker would stop Running,
canceling and releasing the runnable leading to releasing the proxy in an
unclean state. Instead, we AddRef() and add the feature and remove the feature
and Release() on Notify(). If callers successfully run a WorkerRunnable they
clean the proxy. If not, the proxy stays alive until the worker switches to
Canceling state.
The bulk of this commit was generated by running:
run-clang-tidy.py \
-checks='-*,llvm-namespace-comment' \
-header-filter=^/.../mozilla-central/.* \
-fix
