Enable inference in the core libs

test/codegen/expect/dart/_interceptors.js

 var _interceptors;
 (function(exports) {
   'use strict';
   let JSArray$ = dart.generic(function(E) {
     class JSArray extends Interceptor {
       JSArray() {
         super.Interceptor();
       }
       JSArray$fixed(length) {
         if (dart.notNull(!(typeof length == number)) || dart.notNull(length) < 0) {
@@ skipping 1172 matching lines @@
       result.set(_symbolToString(key), value);
     });
     return result;
   }
   // Function getInterceptor: (dynamic) → dynamic
   function getInterceptor(object) {
     return void 0;
   }
   // Function getDispatchProperty: (dynamic) → dynamic
   function getDispatchProperty(object) {
-    return object[_foreign_helper.JS_EMBEDDED_GLOBAL('String', dart.as(_js_embedded_names.DISPATCH_PROPERTY_NAME, core.String))];
+    return object[_foreign_helper.JS_EMBEDDED_GLOBAL('String', _js_embedded_names.DISPATCH_PROPERTY_NAME)];
   }
   // Function setDispatchProperty: (dynamic, dynamic) → dynamic
   function setDispatchProperty(object, value) {
-    _js_helper.defineProperty(object, dart.as(_foreign_helper.JS_EMBEDDED_GLOBAL('String', dart.as(_js_embedded_names.DISPATCH_PROPERTY_NAME, core.String)), core.String), value);
+    _js_helper.defineProperty(object, dart.as(_foreign_helper.JS_EMBEDDED_GLOBAL('String', _js_embedded_names.DISPATCH_PROPERTY_NAME), core.String), value);
   }
   // Function makeDispatchRecord: (dynamic, dynamic, dynamic, dynamic) → dynamic
   function makeDispatchRecord(interceptor, proto, extension, indexability) {
     return {i: interceptor, p: proto, e: extension, x: indexability};
   }
   // Function dispatchRecordInterceptor: (dynamic) → dynamic
   function dispatchRecordInterceptor(record) {
     return record.i;
   }
   // Function dispatchRecordProto: (dynamic) → dynamic
@@ skipping 39 matching lines @@
       if (proto == null || proto === Object.prototype) {
         return _foreign_helper.JS_INTERCEPTOR_CONSTANT(PlainJavaScriptObject);
       } else {
         return _foreign_helper.JS_INTERCEPTOR_CONSTANT(UnknownJavaScriptObject);
       }
     }
     return interceptor;
   }
   dart.copyProperties(exports, {
     get mapTypeToInterceptor() {
-      return _foreign_helper.JS_EMBEDDED_GLOBAL('', dart.as(_js_embedded_names.MAP_TYPE_TO_INTERCEPTOR, core.String));
+      return _foreign_helper.JS_EMBEDDED_GLOBAL('', _js_embedded_names.MAP_TYPE_TO_INTERCEPTOR);
     }
   });
   // Function findIndexForNativeSubclassType: (Type) → int
   function findIndexForNativeSubclassType(type) {
     if (exports.mapTypeToInterceptor == null)
       return null;
     let map = dart.as(exports.mapTypeToInterceptor, core.List);
     for (let i = 0; dart.notNull(i) + 1 < dart.notNull(map.length); i = 3) {
       if (dart.equals(type, map.get(i))) {
         return i;
@@ skipping 142 matching lines @@
   exports.Interceptor = Interceptor;
   exports.JSBool = JSBool;
   exports.JSNull = JSNull;
   exports.JSIndexable = JSIndexable;
   exports.JSMutableIndexable = JSMutableIndexable;
   exports.JSObject = JSObject;
   exports.JavaScriptObject = JavaScriptObject;
   exports.PlainJavaScriptObject = PlainJavaScriptObject;
   exports.UnknownJavaScriptObject = UnknownJavaScriptObject;
 })(_interceptors || (_interceptors = {}));