Add ParameterMirror.isInitializingFormal to dart:mirrors

sdk/lib/_internal/js_runtime/lib/js_helper.dart

Index: sdk/lib/_internal/js_runtime/lib/js_helper.dart
diff --git a/sdk/lib/_internal/js_runtime/lib/js_helper.dart b/sdk/lib/_internal/js_runtime/lib/js_helper.dart
index 2a91a2e34eb8247d1cd3d27c368125f8aa4b176a..c64fc17b670f6e52c69090036761cfd8439b8511 100644
--- a/sdk/lib/_internal/js_runtime/lib/js_helper.dart
+++ b/sdk/lib/_internal/js_runtime/lib/js_helper.dart
@@ -614,6 +614,15 @@ class ReflectionInfo {
     }
   }
 
+  bool isFieldInitializerParameter(int parameter) {
+    if (!JS_GET_FLAG('MUST_RETAIN_METADATA')) {
+      throw new StateError('metadata has not been preserved');
+    } else {
+      return JS('bool', '#[2 * # + 2*# + # + # + 1]', data, parameter,
+          optionalParameterCount, requiredParameterCount, FIRST_DEFAULT_ARGUMENT);
+    }
+  }
+
   int defaultValue(int parameter) {
     if (parameter < requiredParameterCount) return null;
     return JS('int', '#[# + # - #]', data,