simplify function coercions -- DDC can generate function types in place

lib/runtime/dart/_isolate_helper.js

 dart_library.library('dart/_isolate_helper', null, /* Imports */[
   'dart/_runtime',
   'dart/core',
   'dart/_native_typed_data',
   'dart/_interceptors',
   'dart/_js_helper',
   'dart/isolate',
   'dart/_foreign_helper',
   'dart/_js_embedded_names',
   'dart/collection',
@@ skipping 87 matching lines @@
       return serialized;
     }
     serializeArrayInPlace(x) {
       for (let i = 0; i < dart.notNull(x[dartx.length]); i++) {
         x[dartx.set](i, this.serialize(x[dartx.get](i)));
       }
       return x;
     }
     serializeMap(x) {
       let serializeTearOff = dart.bind(this, 'serialize');
-      return dart.list(['map', x[dartx.keys][dartx.map](dart.as(serializeTearOff, __CastType0))[dartx.toList](), x[dartx.values][dartx.map](dart.as(serializeTearOff, dart.functionType(dart.dynamic, [dart.dynamic])))[dartx.toList]()], core.Object);
+      return dart.list(['map', x[dartx.keys][dartx.map](dart.as(serializeTearOff, dart.functionType(dart.dynamic, [dart.dynamic])))[dartx.toList](), x[dartx.values][dartx.map](dart.as(serializeTearOff, dart.functionType(dart.dynamic, [dart.dynamic])))[dartx.toList]()], core.Object);
     }
     serializeJSObject(x) {
       if (!!x.constructor && x.constructor !== Object) {
         this.unsupported(x, "Only plain JS Objects are supported:");
       }
       let keys = dart.as(Object.keys(x), core.List);
       let values = [];
       values[dartx.length] = keys[dartx.length];
       for (let i = 0; i < dart.notNull(keys[dartx.length]); i++) {
         values[dartx.set](i, this.serialize(x[keys[dartx.get](i)]));
@@ skipping 256 matching lines @@
       deserializeMutable: [core.List, [dart.dynamic]],
       deserializeConst: [core.List, [dart.dynamic]],
       deserializeMap: [core.Map, [dart.dynamic]],
       deserializeSendPort: [isolate.SendPort, [dart.dynamic]],
       deserializeRawSendPort: [isolate.SendPort, [dart.dynamic]],
       deserializeJSObject: [dart.dynamic, [dart.dynamic]],
       deserializeClosure: [core.Function, [dart.dynamic]],
       deserializeDartObject: [dart.dynamic, [dart.dynamic]]
     })
   });
-  const __CastType0 = dart.typedef('__CastType0', () => dart.functionType(dart.dynamic, [dart.dynamic]));
   function _callInIsolate(isolate, func) {
     let result = isolate.eval(func);
     exports._globalState.topEventLoop.run();
     return result;
   }
   dart.fn(_callInIsolate, () => dart.definiteFunctionType(dart.dynamic, [_IsolateContext, core.Function]));
   const _activeJsAsyncCount = Symbol('_activeJsAsyncCount');
   function enterJsAsync() {
     let o = exports._globalState.topEventLoop;
     o[_activeJsAsyncCount] = dart.notNull(o[_activeJsAsyncCount]) + 1;
@@ skipping 1112 matching lines @@
   exports.leaveJsAsync = leaveJsAsync;
   exports.isWorker = isWorker;
   exports.startRootIsolate = startRootIsolate;
   exports.IsolateNatives = IsolateNatives;
   exports.RawReceivePortImpl = RawReceivePortImpl;
   exports.ReceivePortImpl = ReceivePortImpl;
   exports.TimerImpl = TimerImpl;
   exports.hasTimer = hasTimer;
   exports.CapabilityImpl = CapabilityImpl;
 });