Fix dynamic calls on JS interop classes.

pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/classes.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /// This library defines the operations that define and manipulate Dart
 /// classes.  Included in this are:
 ///   - Generics
 ///   - Class metadata
 ///   - Extension methods
 ///
@@ skipping 185 matching lines @@
 
 getGenericTypeCtor(value) => JS('', '#[#]', value, _genericTypeCtor);
 
 /// Get the type of a method from an object using the stored signature
 getType(obj) => JS(
     '',
     '''(() => {
   return $obj == null ? $Object : $obj.__proto__.constructor;
 })()''');
 
+bool isJsInterop(obj) {
+  if (JS('bool', 'typeof # === "function"', obj)) {
+    // A function is a Dart function if it has runtime type information.
+    return _getRuntimeType(obj) == null;
+  }
+  // Primitive types are not JS interop types.
+  if (JS('bool', 'typeof # !== "object"', obj)) return false;
+
+  // Extension types are not considered JS interop types.
+  // Note that it is still possible to call typed JS interop methods on
+  // extension types but the calls must be statically typed.
+  if (getExtensionType(obj) != null) return false;
+  return JS('bool', '!($obj instanceof $Object)');
+}
+
 /// Get the type of a method from a type using the stored signature
 getMethodType(type, name) => JS(
     '',
     '''(() => {
   let sigObj = $type[$_methodSig];
   if (sigObj === void 0) return void 0;
   return sigObj[$name];
 })()''');
 
 getFieldType(type, name) => JS(
@@ skipping 403 matching lines @@
     '''(() => {
   let values = [];
   for (var i = 0; i < $names.length; i++) {
     let value = $const_(new $enumClass(i));
     values.push(value);
     Object.defineProperty($enumClass, $names[i],
         { value: value, configurable: true });
   }
   $enumClass.values = $constList(values, $enumClass);
 })()''');