Initializes a polymer application as follows: * if running in development mode, set up a dirty-checking zone that polls
for observable changes
for each library included transitively from HTML and HTML imports, register custom elements declared there (labeled with CustomTag) and invoke the initialization method on it (top-level functions annotated with initMethod).
Future<Zone> initPolymer() {
_initializeLogging();
if (_deployMode) {
return startPolymer().then((_) => Zone.current);
}
return dirtyCheckZone()
.run(() => startPolymer().then((_) => dirtyCheckZone()));
}