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separate the process to initialize environment, and
start the session.

These are necessary step to launch athena in chrome.

BUG=397167

Review URL: https://codereview.chromium.org/485183002

Cr-Commit-Position: refs/heads/master@{#290686}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@290686 0039d316-1c4b-4281-b951-d872f2087c98