Add compiler info to experiment data.

Check the build label to see which compiler was used.  Store the
compiler in the label, and add it to the json filename
and output.

Also update nightly buildbot script to add 'compiler' field to
labels.

BUG=None
TEST=Tested in my directory.

Change-Id: I124c4910cce1145708bb2a52e3a6d6dff93777c3
Reviewed-on: https://chrome-internal-review.googlesource.com/231811
Commit-Ready: Caroline Tice <cmtice@google.com>
Tested-by: Caroline Tice <cmtice@google.com>
Reviewed-by: Caroline Tice <cmtice@google.com>
6 files changed