fix how DDC finds its undefined constant

pkg/dev_compiler/test/codegen_expected/identity_test.js

Index: pkg/dev_compiler/test/codegen_expected/identity_test.js
diff --git a/pkg/dev_compiler/test/codegen_expected/identity_test.js b/pkg/dev_compiler/test/codegen_expected/identity_test.js
index 32beed1f464e29304e08dc6928042f0a78db2caf..254923fc6e0280a98aa5a5aeb1bbd04af047f7c9 100644
--- a/pkg/dev_compiler/test/codegen_expected/identity_test.js
+++ b/pkg/dev_compiler/test/codegen_expected/identity_test.js
@@ -5,6 +5,7 @@ define(['dart_sdk', 'expect'], function(dart_sdk, expect) {
   const dartx = dart_sdk.dartx;
   const minitest = expect.minitest;
   const identity_test = Object.create(null);
+  const $_get = dartx._get;
   let TToT = () => (TToT = dart.constFn(dart.gFnType(T => [T, [T]])))();
   let VoidToT = () => (VoidToT = dart.constFn(dart.gFnType(T => [T, []])))();
   let VoidToNull = () => (VoidToNull = dart.constFn(dart.fnType(core.Null, [])))();
@@ -30,9 +31,11 @@ define(['dart_sdk', 'expect'], function(dart_sdk, expect) {
   identity_test.BluesBrother = class BluesBrother extends core.Object {};
   (identity_test.BluesBrother.new = function() {
   }).prototype = identity_test.BluesBrother.prototype;
+  dart.addTypeTests(identity_test.BluesBrother);
   identity_test._Jake = class _Jake extends identity_test.BluesBrother {};
   (identity_test._Jake.new = function() {
   }).prototype = identity_test._Jake.prototype;
+  dart.addTypeTests(identity_test._Jake);
   identity_test._Elwood = class _Elwood extends identity_test.BluesBrother {
     ['=='](other) {
       return identity_test._Elwood.is(other);
@@ -40,12 +43,14 @@ define(['dart_sdk', 'expect'], function(dart_sdk, expect) {
   };
   (identity_test._Elwood.new = function() {
   }).prototype = identity_test._Elwood.prototype;
+  dart.addTypeTests(identity_test._Elwood);
   dart.setSignature(identity_test._Elwood, {
     methods: () => ({'==': dart.fnType(core.bool, [core.Object])})
   });
   identity_test._Norman = class _Norman extends identity_test.BluesBrother {};
   (identity_test._Norman.new = function() {
   }).prototype = identity_test._Norman.prototype;
+  dart.addTypeTests(identity_test._Norman);
   identity_test.hideNull = function(T) {
     return x => {
       return x;
@@ -54,7 +59,7 @@ define(['dart_sdk', 'expect'], function(dart_sdk, expect) {
   dart.fn(identity_test.hideNull, TToT());
   identity_test.getUndefined = function(T) {
     return () => {
-      return T._check(core.List.new(1)[dartx._get](0));
+      return T._check(core.List.new(1)[$_get](0));
     };
   };
   dart.fn(identity_test.getUndefined, VoidToT());