fix #29182, generate top level const fields lazily

pkg/dev_compiler/test/codegen_expected/destructuring.js

Index: pkg/dev_compiler/test/codegen_expected/destructuring.js
diff --git a/pkg/dev_compiler/test/codegen_expected/destructuring.js b/pkg/dev_compiler/test/codegen_expected/destructuring.js
index c8fb9e5f50fe530eddfb42a35f504959c69c771b..e3004f5138c8e936599467cbcb6dcd199373491e 100644
--- a/pkg/dev_compiler/test/codegen_expected/destructuring.js
+++ b/pkg/dev_compiler/test/codegen_expected/destructuring.js
@@ -75,7 +75,11 @@ define(['dart_sdk'], function(dart_sdk) {
     new() {
     }
   };
-  src__varargs.rest = dart.const(new src__varargs._Rest());
+  dart.defineLazy(src__varargs, {
+    get rest() {
+      return dart.const(new src__varargs._Rest());
+    }
+  });
   src__varargs.spread = function(args) {
     dart.throw(new core.StateError('The spread function cannot be called, ' + 'it should be compiled away.'));
   };