metricsd: Create a brillo::MessageLoop.

brillo::BinderWatcher now requires a brillo::MessageLoop, so this patch
creates a brillo::BaseMessageLoop and passes it when creating the
brillo::BinderWatcher.

Bug: 26356682
TEST=Deployed metricsd to edison-eng.

Change-Id: I6a9e592623faf231205ae44e479bec2b873b8898
2 files changed