Add Capability class.

sdk/lib/_internal/lib/isolate_patch.dart

Index: sdk/lib/_internal/lib/isolate_patch.dart
diff --git a/sdk/lib/_internal/lib/isolate_patch.dart b/sdk/lib/_internal/lib/isolate_patch.dart
index 45de5af4ccf117ea1c12053333ae84a7bf7eeef6..4ad59ca943fd54b364e716ca3dac97479a2360eb 100644
--- a/sdk/lib/_internal/lib/isolate_patch.dart
+++ b/sdk/lib/_internal/lib/isolate_patch.dart
@@ -54,3 +54,9 @@ patch class RawReceivePort {
     return new RawReceivePortImpl(handler);
   }
 }
+
+patch class Capability {
+  patch factory Capability() {
+    throw new UnimplementedError();
+  }
+}