Reify type params on map literals

test/codegen_expected/language/map_literal2_test.js

 dart_library.library('language/map_literal2_test', null, /* Imports */[
   'dart_sdk',
   'expect'
 ], function load__map_literal2_test(exports, dart_sdk, expect) {
   'use strict';
   const core = dart_sdk.core;
   const dart = dart_sdk.dart;
   const dartx = dart_sdk.dartx;
   const expect$ = expect.expect;
   const map_literal2_test = Object.create(null);
   let VoidTodynamic = () => (VoidTodynamic = dart.constFn(dart.definiteFunctionType(dart.dynamic, [])))();
   map_literal2_test.nextValCtr = null;
   dart.copyProperties(map_literal2_test, {
     get nextVal() {
       let x = map_literal2_test.nextValCtr;
       map_literal2_test.nextValCtr = dart.notNull(x) + 1;
       return x;
     }
   });
   map_literal2_test.main = function() {
     map_literal2_test.nextValCtr = 0;
-    let map = dart.map({[dart.str`a${map_literal2_test.nextVal}`]: "Grey", [dart.str`a${map_literal2_test.nextVal}`]: "Poupon"});
+    let map = dart.map({[dart.str`a${map_literal2_test.nextVal}`]: "Grey", [dart.str`a${map_literal2_test.nextVal}`]: "Poupon"}, core.String, core.String);
     expect$.Expect.equals(true, map[dartx.containsKey]("a0"));
     expect$.Expect.equals(true, map[dartx.containsKey]("a1"));
     expect$.Expect.equals("Grey", map[dartx.get]("a0"));
     expect$.Expect.equals("Poupon", map[dartx.get]("a1"));
   };
   dart.fn(map_literal2_test.main, VoidTodynamic());
   // Exports:
   exports.map_literal2_test = map_literal2_test;
 });