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This CL enables the user to launch the chrome remote desktop app directly into an immersive it2me helper session.
In the immersive session, the app will
1. hide the home screen
2. create an hrd_helper_session object to communicate with the it2me_background service.

Review URL: https://codereview.chromium.org/439923002

Cr-Commit-Position: refs/heads/master@{#288466}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@288466 0039d316-1c4b-4281-b951-d872f2087c98