- Add a minimal implementation of Capability.

runtime/vm/snapshot.h

Index: runtime/vm/snapshot.h
===================================================================
--- runtime/vm/snapshot.h	(revision 35287)
+++ runtime/vm/snapshot.h	(working copy)
@@ -57,6 +57,9 @@
 class RawPatchClass;
 class RawScript;
 class RawSmi;
+class RawCapability;
+class RawReceivePort;
+class RawSendPort;
 class RawStacktrace;
 class RawTokenStream;
 class RawType;
@@ -548,6 +551,7 @@
   friend class RawJSRegExp;
   friend class RawLibrary;
   friend class RawLiteralToken;
+  friend class RawReceivePort;
   friend class RawScript;
   friend class RawStacktrace;
   friend class RawTokenStream;