We changed the bootstrap order:
1. create NgZone
2. bootstrap ng1 inside NgZone and upgrade ng1 components to ng2 components.
3. bootstrap ng2 with NgZone
Note: Previous footgun behavior was: bootstrap ng2 first to extract NgZone, so that ng1 bootstrap can happen in NgZone. This meant that if ng2 bootstrap eagerly compiled a component which contained ng1 components, then we did not have complete metadata.
