FakeCryptohomeClient returns empty strings for calls returning data. Many of these strings represent serialized protos, and therefore callers of FakeCryptohomeClient (typically indirectly through stubbing, but also in unit tests) cannot to much, including very basic operations.

This bug is a tracker for a number of different improvements that can be done to FakeCryptohomeClient which will allow some stubbed flows to work better during development and improve tests.