fix how DDC finds its undefined constant

pkg/dev_compiler/test/codegen_expected/destructuring.js

 define(['dart_sdk'], function(dart_sdk) {
   'use strict';
   const core = dart_sdk.core;
   const dart = dart_sdk.dart;
   const dartx = dart_sdk.dartx;
   const destructuring = Object.create(null);
   const src__varargs = Object.create(null);
   let intAnddynamic__Todynamic = () => (intAnddynamic__Todynamic = dart.constFn(dart.fnType(dart.dynamic, [core.int, dart.dynamic], [dart.dynamic])))();
   let intAnddynamic__Todynamic$ = () => (intAnddynamic__Todynamic$ = dart.constFn(dart.fnType(dart.dynamic, [core.int, dart.dynamic], {c: dart.dynamic})))();
   let intAnddynamicTodynamic = () => (intAnddynamicTodynamic = dart.constFn(dart.fnType(dart.dynamic, [core.int, dart.dynamic])))();
   let intAnddynamicAnddynamicTodynamic = () => (intAnddynamicAnddynamicTodynamic = dart.constFn(dart.fnType(dart.dynamic, [core.int, dart.dynamic, dart.dynamic])))();
   let __Todynamic = () => (__Todynamic = dart.constFn(dart.fnType(dart.dynamic, [], [core.int, dart.dynamic, dart.dynamic])))();
   let __Todynamic$ = () => (__Todynamic$ = dart.constFn(dart.fnType(dart.dynamic, [], {let: core.int, function: dart.dynamic, arguments: dart.dynamic})))();
   let __Todynamic$0 = () => (__Todynamic$0 = dart.constFn(dart.fnType(dart.dynamic, [], {constructor: core.int, valueOf: dart.dynamic, hasOwnProperty: dart.dynamic})))();
   let dynamicTodynamic = () => (dynamicTodynamic = dart.constFn(dart.fnType(dart.dynamic, [dart.dynamic])))();
-  destructuring.f = function(a, b, c = 1) {
+  destructuring.f = function(a = null, b = null, c = 1) {
     destructuring.f(a, b, c);
   };
   dart.fn(destructuring.f, intAnddynamic__Todynamic());
   destructuring.f_sync = function(a, b, c) {
-    return dart.syncStar(function*(a, b, c = 1) {
+    return dart.syncStar(function*(a = null, b = null, c = 1) {
     }, dart.dynamic, a, b, c);
   };
   dart.fn(destructuring.f_sync, intAnddynamic__Todynamic());
   destructuring.f_async = function(a, b, c) {
-    return dart.asyncStar(function*(stream, a, b, c = 1) {
+    return dart.asyncStar(function*(stream, a = null, b = null, c = 1) {
     }, dart.dynamic, a, b, c);
   };
   dart.fn(destructuring.f_async, intAnddynamic__Todynamic());
-  destructuring.g = function(a, b, {c = 1} = {}) {
+  destructuring.g = function(a = null, b = null, {c = 1} = {}) {
     destructuring.f(a, b, c);
   };
   dart.fn(destructuring.g, intAnddynamic__Todynamic$());
   destructuring.g_sync = function(a, b, opts) {
-    return dart.syncStar(function*(a, b, {c = 1} = {}) {
+    return dart.syncStar(function*(a = null, b = null, {c = 1} = {}) {
     }, dart.dynamic, a, b, opts);
   };
   dart.fn(destructuring.g_sync, intAnddynamic__Todynamic$());
   destructuring.g_async = function(a, b, opts) {
-    return dart.asyncStar(function*(stream, a, b, {c = 1} = {}) {
+    return dart.asyncStar(function*(stream, a = null, b = null, {c = 1} = {}) {
     }, dart.dynamic, a, b, opts);
   };
   dart.fn(destructuring.g_async, intAnddynamic__Todynamic$());
-  destructuring.r = function(a, ...others) {
+  destructuring.r = function(a = null, ...others = null) {
     destructuring.r(a, ...others);
   };
   dart.fn(destructuring.r, intAnddynamicTodynamic());
   destructuring.r_sync = function(a, ...others) {
-    return dart.syncStar(function*(a, ...others) {
+    return dart.syncStar(function*(a = null, ...others = null) {
     }, dart.dynamic, a, ...others);
   };
   dart.fn(destructuring.r_sync, intAnddynamicTodynamic());
   destructuring.r_async = function(a, ...others) {
-    return dart.asyncStar(function*(stream, a, ...others) {
+    return dart.asyncStar(function*(stream, a = null, ...others = null) {
     }, dart.dynamic, a, ...others);
   };
   dart.fn(destructuring.r_async, intAnddynamicTodynamic());
-  destructuring.invalid_names1 = function(let$, func, arguments$) {
+  destructuring.invalid_names1 = function(let$ = null, func = null, arguments$ = null) {
     destructuring.f(let$, func, arguments$);
   };
   dart.fn(destructuring.invalid_names1, intAnddynamicAnddynamicTodynamic());
   destructuring.invalid_names2 = function(let$ = null, func = 1, arguments$ = null) {
     destructuring.f(let$, func, arguments$);
   };
   dart.fn(destructuring.invalid_names2, __Todynamic());
   destructuring.invalid_names3 = function({["let"]: let$ = null, ["function"]: func = null, ["arguments"]: arguments$ = 2} = {}) {
     destructuring.f(let$, func, arguments$);
   };
   dart.fn(destructuring.invalid_names3, __Todynamic$());
   destructuring.names_clashing_with_object_props = function({constructor = null, valueOf = null, hasOwnProperty = 2} = Object.create(null)) {
     destructuring.f(constructor, valueOf, hasOwnProperty);
   };
   dart.fn(destructuring.names_clashing_with_object_props, __Todynamic$0());
   src__varargs._Rest = class _Rest extends core.Object {};
   (src__varargs._Rest.new = function() {
   }).prototype = src__varargs._Rest.prototype;
+  dart.addTypeTests(src__varargs._Rest);
   dart.defineLazy(src__varargs, {
     get rest() {
       return dart.const(new src__varargs._Rest.new());
     }
   });
-  src__varargs.spread = function(args) {
+  src__varargs.spread = function(args = null) {
     dart.throw(new core.StateError.new('The spread function cannot be called, ' + 'it should be compiled away.'));
   };
   dart.fn(src__varargs.spread, dynamicTodynamic());
   dart.trackLibraries("destructuring", {
     "destructuring.dart": destructuring,
     "package:js/src/varargs.dart": src__varargs
   }, null);
   // Exports:
   return {
     destructuring: destructuring,
     src__varargs: src__varargs
   };
 });