Change mojo_public_bindings_unittests to use chromium environment.
This is needed by the associated interface implementation, which uses
base::MessageLoop and related classes. It won't work with the standalone
environment, and we want to stop using the standalone environment anyway.
BUG=
546067
Committed:
https://crrev.com/70bfaf3f892dcfe48e980c01e22422226816f717
Cr-Commit-Position: refs/heads/master@{#358146}