Add the --disable-off-store-extension-install switch.

Subsequent changes will add a first-class UI in chrome://extensions/
to meet this use case.

BUG=55584

Review URL: https://chromiumcodereview.appspot.com/10266015

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@134980 0039d316-1c4b-4281-b951-d872f2087c98
9 files changed