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Without this change, the content shell would crash after pressing back
to the home screen and relaunching.  The two problems this fixes are:

1.) It was trying to initialize the command line even though it already
    was init'ed before.
2.) The shell wasn't being recreated because it is done during process
    start and the process is already running.

BUG=
TEST=


Review URL: https://chromiumcodereview.appspot.com/10701177

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@148365 0039d316-1c4b-4281-b951-d872f2087c98