Bug 1048937 - Implement  'share' option in system browser. r=vingtetun,kgrandon

(moving this comment) For future tests we may want to just use a more simple mock server without E.me stubs, but since this is already done it's probably fine for now. For the next test, unless we need to explicitly test E.me code, let's use the simple server here with a small fixture: https://github.com/mozilla-b2g/gaia/blob/master/shared/test/integration/server.js