Allow expansion flags to have values.

This lets us change what it expands based on the argument passed to the flag.

RELNOTES: Allows flags that expand to take values.
PiperOrigin-RevId: 160298412
GitOrigin-RevId: 7c7255ec8d6da20526c2c4078c57aadaf3dd3612
Change-Id: I4e6d8d79a13ea89329d52280958122fa01e91872
8 files changed
tree: 001b043828326d7685cc3498137ce1dfef09d76b
  1. java/