GitLab

- Introduces a new scheme "exe" which loads an executable alongside mojo_runner. TODO is some more security checking around this to prevent arbitrary apps from launching executables but since this is implemented in mojo_runner it's not in any production code right now.
- Includes an apptest of a .mojo app that connects to an executable and binds a service provided by it.
- Creates a new child library that makes it easy to bring up a runner controller thread in an arbitrary executable.

R=jam@chromium.org
http://crbug.com/548694

Review URL: https://codereview.chromium.org/1419293003

Cr-Commit-Position: refs/heads/master@{#357034}