Enable inference in the core libs

test/codegen/expect/dart/_js_names.js

 var _js_names;
 (function(exports) {
   'use strict';
   // Function preserveNames: () → dynamic
   function preserveNames() {
   }
   dart.defineLazyProperties(exports, {
     get mangledNames() {
-      return computeMangledNames(_foreign_helper.JS_EMBEDDED_GLOBAL('=Object', dart.as(_js_embedded_names.MANGLED_NAMES, core.String)), false);
+      return computeMangledNames(_foreign_helper.JS_EMBEDDED_GLOBAL('=Object', _js_embedded_names.MANGLED_NAMES), false);
     },
     get reflectiveNames() {
       return computeReflectiveNames(exports.mangledNames);
     },
     get mangledGlobalNames() {
-      return computeMangledNames(_foreign_helper.JS_EMBEDDED_GLOBAL('=Object', dart.as(_js_embedded_names.MANGLED_GLOBAL_NAMES, core.String)), true);
+      return computeMangledNames(_foreign_helper.JS_EMBEDDED_GLOBAL('=Object', _js_embedded_names.MANGLED_GLOBAL_NAMES), true);
     },
     get reflectiveGlobalNames() {
       return computeReflectiveNames(exports.mangledGlobalNames);
     }
   });
   // Function computeMangledNames: (dynamic, bool) → Map<String, String>
   function computeMangledNames(jsMangledNames, isGlobal) {
     preserveNames();
     let keys = extractKeys(jsMangledNames);
     let result = dart.map();
@@ skipping 27 matching lines @@
       for (var key in victim) {
         if (hasOwnProperty.call(victim, key))
           result.push(key);
       }
       return result;
     }(victim, Object.prototype.hasOwnProperty);
     return new _interceptors.JSArray.markFixed(result);
   }
   // Function unmangleGlobalNameIfPreservedAnyways: (String) → String
   function unmangleGlobalNameIfPreservedAnyways(name) {
-    let names = _foreign_helper.JS_EMBEDDED_GLOBAL('=Object', dart.as(_js_embedded_names.MANGLED_GLOBAL_NAMES, core.String));
+    let names = _foreign_helper.JS_EMBEDDED_GLOBAL('=Object', _js_embedded_names.MANGLED_GLOBAL_NAMES);
     return dart.as(_js_helper.JsCache.fetch(names, name), core.String);
   }
   // Function unmangleAllIdentifiersIfPreservedAnyways: (String) → String
   function unmangleAllIdentifiersIfPreservedAnyways(str) {
     return str.replace(/[^<,> ]+/g, function(m) {
-      return _foreign_helper.JS_EMBEDDED_GLOBAL('', dart.as(_js_embedded_names.MANGLED_GLOBAL_NAMES, core.String))[m] || m;
+      return _foreign_helper.JS_EMBEDDED_GLOBAL('', _js_embedded_names.MANGLED_GLOBAL_NAMES)[m] || m;
     });
   }
   // Exports:
   exports.preserveNames = preserveNames;
   exports.computeMangledNames = computeMangledNames;
   exports.computeReflectiveNames = computeReflectiveNames;
   exports.extractKeys = extractKeys;
   exports.unmangleGlobalNameIfPreservedAnyways = unmangleGlobalNameIfPreservedAnyways;
   exports.unmangleAllIdentifiersIfPreservedAnyways = unmangleAllIdentifiersIfPreservedAnyways;
 })(_js_names || (_js_names = {}));