Cherry-Pick: Don't assume that uid_t is int

When libchrome is compiled in Brillo, using Android bionic, uid_t is
actually defined as 'unsigned int'.

This is Chromium r260569, and is the sole code fix required to allow
building the Fluoride unit tests and test tools for a Mac host.

BUG=22771504, chromium:534675

Change-Id: I16e5ab954d1fb8540c0b875ce6b31d48a787a612
1 file changed