GitLab

This CL
- Introduces an It2MeService component that listens to incoming connection requests between Hangouts and the webapp and establish a channel between them.
- It enables launching an IT2Me helper session from Hangouts

Review URL: https://codereview.chromium.org/468693002

Cr-Commit-Position: refs/heads/master@{#289538}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@289538 0039d316-1c4b-4281-b951-d872f2087c98