fix how DDC finds its undefined constant

pkg/dev_compiler/test/codegen_expected/node_modules.js

 'use strict';
 const dart_sdk = require('dart_sdk');
 const core = dart_sdk.core;
 const dart = dart_sdk.dart;
 const dartx = dart_sdk.dartx;
 const node_modules = Object.create(null);
 let B = () => (B = dart.constFn(node_modules.B$()))();
 let _B = () => (_B = dart.constFn(node_modules._B$()))();
 let VoidTodynamic = () => (VoidTodynamic = dart.constFn(dart.fnType(dart.dynamic, [])))();
 let VoidToString = () => (VoidToString = dart.constFn(dart.fnType(core.String, [])))();
 node_modules.Callback = dart.typedef('Callback', () => dart.fnTypeFuzzy(dart.void, [], {i: core.int}));
 node_modules.A = class A extends core.Object {};
 (node_modules.A.new = function() {
 }).prototype = node_modules.A.prototype;
+dart.addTypeTests(node_modules.A);
 node_modules._A = class _A extends core.Object {};
 (node_modules._A.new = function() {
 }).prototype = node_modules._A.prototype;
+dart.addTypeTests(node_modules._A);
+const _is_B_default = Symbol('_is_B_default');
 node_modules.B$ = dart.generic(T => {
   class B extends core.Object {}
   (B.new = function() {
   }).prototype = B.prototype;
   dart.addTypeTests(B);
+  B.prototype[_is_B_default] = true;
   return B;
 });
 node_modules.B = B();
+dart.addTypeTests(node_modules.B, _is_B_default);
+const _is__B_default = Symbol('_is__B_default');
 node_modules._B$ = dart.generic(T => {
   class _B extends core.Object {}
   (_B.new = function() {
   }).prototype = _B.prototype;
   dart.addTypeTests(_B);
+  _B.prototype[_is__B_default] = true;
   return _B;
 });
 node_modules._B = _B();
+dart.addTypeTests(node_modules._B, _is__B_default);
 node_modules.f = function() {
 };
 dart.fn(node_modules.f, VoidTodynamic());
 node_modules._f = function() {
 };
 dart.fn(node_modules._f, VoidTodynamic());
 dart.defineLazy(node_modules, {
   get constant() {
     return "abc";
   },
@@ skipping 16 matching lines @@
       return "abc";
     }, VoidToString())();
   },
   set lazyMutable(_) {}
 });
 dart.trackLibraries("node_modules", {
   "node_modules.dart": node_modules
 }, null);
 // Exports:
 exports.node_modules = node_modules;