Revert r251578. I was in the middle of editing the commit message

and decided to not commit the change, but accidentally committed
it anyway.

This was based on a static analysis complaint; it thought there
was a code path where AdbClient::PushFile would call AdbClient::ReadSyncHeader
and AdbClient::ReadSyncHeader wouldn't set data_len.  But in that
case, the Error object returned will be Fail and we won't use
the data_len or response_id contents.

llvm-svn: 251580