Enable inference in the core libs

test/dart_codegen/expect/async/zone.dart

 part of dart.async;
  typedef dynamic ZoneCallback();
  typedef dynamic ZoneUnaryCallback(arg);
  typedef dynamic ZoneBinaryCallback(arg1, arg2);
  typedef dynamic HandleUncaughtErrorHandler(Zone self, ZoneDelegate parent, Zone zone, error, StackTrace stackTrace);
  typedef dynamic RunHandler(Zone self, ZoneDelegate parent, Zone zone, f());
  typedef dynamic RunUnaryHandler(Zone self, ZoneDelegate parent, Zone zone, f(arg), arg);
  typedef dynamic RunBinaryHandler(Zone self, ZoneDelegate parent, Zone zone, f(arg1, arg2), arg1, arg2);
  typedef ZoneCallback RegisterCallbackHandler(Zone self, ZoneDelegate parent, Zone zone, f());
  typedef ZoneUnaryCallback RegisterUnaryCallbackHandler(Zone self, ZoneDelegate parent, Zone zone, f(arg));
@@ skipping 61 matching lines @@
  ZoneBinaryCallback registerBinaryCallback(Zone zone, f(arg1, arg2));
  AsyncError errorCallback(Zone zone, Object error, StackTrace stackTrace);
  void scheduleMicrotask(Zone zone, f());
  Timer createTimer(Zone zone, Duration duration, void f());
  Timer createPeriodicTimer(Zone zone, Duration period, void f(Timer timer));
  void print(Zone zone, String line);
  Zone fork(Zone zone, ZoneSpecification specification, Map zoneValues);
 }
  abstract class Zone {Zone._();
  static const Zone ROOT = _ROOT_ZONE;
- static Zone _current = DEVC$RT.cast(_ROOT_ZONE, dynamic, Zone, "CastGeneral", """line 262, column 26 of dart:async/zone.dart: """, _ROOT_ZONE is Zone, true);
+ static Zone _current = _ROOT_ZONE;
  static Zone get current => _current;
  dynamic handleUncaughtError(error, StackTrace stackTrace);
  Zone get parent;
  Zone get errorZone;
  bool inSameErrorZone(Zone otherZone);
  Zone fork({
 ZoneSpecification specification, Map zoneValues}
 );
  dynamic run(f());
  dynamic runUnary(f(arg), var arg);
@@ skipping 581 matching lines @@
  typedef __t212 __t206(Zone __u207, ZoneDelegate __u208, Zone __u209, dynamic __u210(dynamic __u211));
  typedef dynamic __t222(dynamic __u223, dynamic __u224);
  typedef __t222 __t215(Zone __u216, ZoneDelegate __u217, Zone __u218, dynamic __u219(dynamic __u220, dynamic __u221));
  typedef AsyncError __t226(Zone __u227, ZoneDelegate __u228, Zone __u229, Object __u230, StackTrace __u231);
  typedef void __t233(Zone __u234, ZoneDelegate __u235, Zone __u236, dynamic __u237());
  typedef Timer __t239(Zone __u240, ZoneDelegate __u241, Zone __u242, Duration __u243, void __u244());
  typedef Timer __t246(Zone __u247, ZoneDelegate __u248, Zone __u249, Duration __u250, void __u251(Timer __u252));
  typedef void __t254(Zone __u255, ZoneDelegate __u256, Zone __u257, String __u258);
  typedef Zone __t260(Zone __u261, ZoneDelegate __u262, Zone __u263, ZoneSpecification __u264, Map<dynamic, dynamic> __u265);
  typedef void __t282(Timer __u283);