We're currently in a transition between using main.sky and main.dart
files as our main() entry point for Sky applications.
This CL makes this runtime controlable by path name. If it finds
a .dart in the path name it will use SkyView, otherwise it will
fall back to the existing WebView codepath.
SkyView does not expose a window object and much of the existing
Sky Engine is not initialized when main() is run. Clients should
be transitioning away from main.sky towards main.dart in the near
future, however main.dart is probably not ready for general
consumption at this point.
R=ianh@google.com
Review URL: https://codereview.chromium.org/1152313002
8aa3caf350