Baseline: 4f5e325e337957ebea139dc52a00027acbbb572f

Cherry picks:

   + 442155f19f2c2764839327c8be3d3ab70edf1910:
     Automated rollback of commit
     a0a0d09debd090fbe74bba59b5d6d3107aaf97e9.

Important changes:

  - Aspects can now define and use exec groups using the same API as
    rules.

This release contains contributions from many people at Google, as well as Kaiqin Chen.