FilesController: switch to posting events to EventBus rather than calling delegate's API

This will be used in SparkPolymerUI to adjust the UI based on what it selected (e.g. disable Push To Chrome Web Store for non-Chrome apps).
Merge remote-tracking branch 'upstream/master' into switch-file-controller-to-event-bus
Merge remote-tracking branch 'upstream/master' into switch-file-controller-to-event-bus

Conflicts:
	ide/app/lib/editors.dart
	ide/app/test/event_bus_test.dart
Manual merge with EventBus changes
Merge remote-tracking branch 'upstream/master' into switch-file-controller-to-event-bus

Conflicts:
	ide/app/lib/event_bus.dart
Renaming
Merge pull request #1641 from ussuri/switch-file-controller-to-event-bus

Switch FilesController over from dedicated delegate to EventBus for notifying listeners