e10s updates (zombie)

- tried to land bug 1023326 yesterday, record-breaking 100+ test failures
  - though only 4 were my fault, rest were "unexpected tabs"
- made a simple async Sandbox api (bug 1028718) and adapted all the tests
  - the test code is not very.. "elegant".. any hints? helpers?
  - fixing up async content/worker on top of that, looking good!

previous weeks