Merge remote-tracking branch 'aosp/upstream' into master

* aosp/upstream:
  Add MutatorName to mutator contexts
  Make off-the-shelf order funcs public.
  Optimize ninjaString.ValueWithEscaper
  Remove go 1.9 testing
  Put the primary builder into the console pool

Bug: 136473661
Test: m checkbuild
Change-Id: I68c80ebb3466fc4544b73e97ee1d2dd1d73b4c77