After processing the string loaded from a file, don't process message
queues. Otherwise, stack traces generated in any processed task will
contain the stack trace of the load. This also introduces
nondeterminism, since it depends on the timing whether something will
be processed inside the load or outside.

Drive-by: Introduce enums for the different bools, to make their
meaning more obvious at call sites.

R=yangguo@chromium.org
CC=herhut@chromium.org

Change-Id: Ib48ee01be8c443a2a408ecb1c9e34bb9ba5a8fe7
Reviewed-on: https://chromium-review.googlesource.com/964141Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51952}