Make registerPassthroughClient() synchronous.

And remove the PID argument.

Bug: 37730021
Test: lshal shows passthrough clients again
Merged-In: I0bee20ae5cde36dbc86662654d0ac9e9489bf0a2
Change-Id: I0bee20ae5cde36dbc86662654d0ac9e9489bf0a2
2 files changed