Baseline: 8f0034ce1e7854521e259a5eaf71859b1e6f95bc

Cherry picks:

   + a9465dfa4b124e331b8bb3e8d0219ea3dff7cdb1:
     Automated rollback of commit
     240af807c935225d98b630666000cc03934f2ce7.

Important changes:

  - Allow specialization to work with constraint_values.

This release contains contributions from many people at Google, as well as Brentley Jones, Fabian Meumertzheim, Keith Smiley, Noa Resare, Sahin Yort, Thomas Zayouna, Vasilios Pantazopoulos.