trunk-tracking: update to r3508

No major changes that we need to be compatible with.  r3508 tweaks
InPlaceResourceRecorder::DoneAndSetHeaders so that we can now make sure to
release it: the recorder is allocated in ps_in_place_check_header_filter and
released in ps_in_place_body_filter, but if there's an error in between it will
be leaked.  We know ps_release_request_context will get run regardless because
it's set as a cleanup handler, so clean up the recorder there.

Fixes #527
Merge pull request #531 from pagespeed/jefftk-update-trunk-tracking

trunk-tracking: update to r3508