fix navigation when deleting project
address comments
Merge pull request #3508 from keertip/nav

fix navigation when deleting project
fix a checked mode issues with preferences.dart
Merge pull request #3509 from devoncarew/devoncarew_prefs_types

fix a checked mode issues with preferences.dart
Started moving NavigationManager to using ContentProviders
Merge branch 'master' of https://github.com/dart-lang/chromedeveditor into umop-preferences-editor_with_providers