Add constructors to signatures

lib/runtime/dart/_foreign_helper.js

 var _foreign_helper = dart.defineLibrary(_foreign_helper, {});
 var core = dart.import(core);
 (function(exports, core) {
   'use strict';
   function JS(typeDescription, codeTemplate, arg0, arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8, arg9, arg10, arg11) {
     if (arg0 === void 0)
       arg0 = null;
     if (arg1 === void 0)
       arg1 = null;
     if (arg2 === void 0)
@@ skipping 99 matching lines @@
   dart.fn(JS_GET_FLAG, core.bool, [core.String]);
   function JS_EFFECT(code) {
     dart.dcall(code, null);
   }
   dart.fn(JS_EFFECT, dart.void, [core.Function]);
   class JS_CONST extends core.Object {
     JS_CONST(code) {
       this.code = code;
     }
   }
+  dart.setSignature(JS_CONST, {
+    constructors: () => ({JS_CONST: [JS_CONST, [core.String]]})
+  });
   function JS_STRING_CONCAT(a, b) {
     return a + b;
   }
   dart.fn(JS_STRING_CONCAT, core.String, [core.String, core.String]);
   // Exports:
   exports.JS = JS;
   exports.JS_CURRENT_ISOLATE_CONTEXT = JS_CURRENT_ISOLATE_CONTEXT;
   exports.IsolateContext = IsolateContext;
   exports.JS_CALL_IN_ISOLATE = JS_CALL_IN_ISOLATE;
   exports.DART_CLOSURE_TO_JS = DART_CLOSURE_TO_JS;
@@ skipping 17 matching lines @@
   exports.JS_FUNCTION_TYPE_REQUIRED_PARAMETERS_TAG = JS_FUNCTION_TYPE_REQUIRED_PARAMETERS_TAG;
   exports.JS_FUNCTION_TYPE_OPTIONAL_PARAMETERS_TAG = JS_FUNCTION_TYPE_OPTIONAL_PARAMETERS_TAG;
   exports.JS_FUNCTION_TYPE_NAMED_PARAMETERS_TAG = JS_FUNCTION_TYPE_NAMED_PARAMETERS_TAG;
   exports.JS_GET_NAME = JS_GET_NAME;
   exports.JS_EMBEDDED_GLOBAL = JS_EMBEDDED_GLOBAL;
   exports.JS_GET_FLAG = JS_GET_FLAG;
   exports.JS_EFFECT = JS_EFFECT;
   exports.JS_CONST = JS_CONST;
   exports.JS_STRING_CONCAT = JS_STRING_CONCAT;
 })(_foreign_helper, core);