Embed a mojo ApplicationManager in content/browser

This embeds mojo/shell's ApplicationManager in content/browser
and provides a way for arbitrary browser code to connect to
Mojo apps as if the browser itself were a Mojo app.

This is a basic implementation of Mojo app support which only
loads static apps either in the browser process or a (per-app)
utility process.

Future CLs will address connection to apps from arbitrary render
frames (i.e. connection requests which include the requestor's
origin) as well as refactoring the utility process code further
so that it serves strictly as a Mojo app runner.

BUG=492422

Review URL: https://codereview.chromium.org/1149833007

Cr-Commit-Position: refs/heads/master@{#332974}
48 files changed