Check in codegen test expectations.

test/codegen/expect/language/map_literal_syntax_test.js

+dart_library.library('language/map_literal_syntax_test', null, /* Imports */[
+  'dart_sdk',
+  'expect'
+], function load__map_literal_syntax_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_literal_syntax_test = Object.create(null);
+  let VoidTodynamic = () => (VoidTodynamic = dart.constFn(dart.definiteFunctionType(dart.dynamic, [])))();
+  let const$;
+  let const$0;
+  map_literal_syntax_test.Foo = class Foo extends core.Object {
+    new() {
+      this.x = dart.map();
+      this.y = dart.map({}, core.String, core.int);
+      this.z = const$ || (const$ = dart.const(dart.map()));
+      this.v = const$0 || (const$0 = dart.const(dart.map({}, core.String, core.int)));
+    }
+  };
+  dart.setSignature(map_literal_syntax_test.Foo, {
+    constructors: () => ({new: dart.definiteFunctionType(map_literal_syntax_test.Foo, [])})
+  });
+  map_literal_syntax_test.main = function() {
+    expect$.Expect.equals("{}", dart.toString(new map_literal_syntax_test.Foo().x));
+    expect$.Expect.equals("{}", dart.toString(new map_literal_syntax_test.Foo().y));
+    expect$.Expect.equals("{}", dart.toString(new map_literal_syntax_test.Foo().z));
+    expect$.Expect.equals("{}", dart.toString(new map_literal_syntax_test.Foo().v));
+  };
+  dart.fn(map_literal_syntax_test.main, VoidTodynamic());
+  // Exports:
+  exports.map_literal_syntax_test = map_literal_syntax_test;
+});