Implement `.instanceMembers`.

reflectable/lib/src/reflectable_implementation.dart

Index: reflectable/lib/src/reflectable_implementation.dart
diff --git a/reflectable/lib/src/reflectable_implementation.dart b/reflectable/lib/src/reflectable_implementation.dart
index 530e297843c8de2d22eb7915fb019c09ea0c1e0d..4908c06c729ce2879f18795cb452f0734953dab3 100644
--- a/reflectable/lib/src/reflectable_implementation.dart
+++ b/reflectable/lib/src/reflectable_implementation.dart
@@ -492,6 +492,11 @@ class _ClassMirrorImpl extends _TypeMirrorImpl with _ObjectMirrorImplMixin
         (Symbol nameSymbol, dm.DeclarationMirror declarationMirror) {
       String name = dm.MirrorSystem.getName(nameSymbol);
       if (declarationMirror is dm.MethodMirror) {
+        if (declarationMirror.isAbstract) {
+          // Dart2js implementation of dart:mirrors does not include abstract
+          // members in declarations. We choose to go the same route.
+          return;
+        }
         if ((declarationMirror.isStatic &&
                 reflectableSupportsStaticInvoke(_reflectable, name)) ||
             reflectableSupportsInstanceInvoke(