Added API Dart_PostCMessage for posting a Dart_CMessage structure

runtime/bin/dartutils.h

Index: runtime/bin/dartutils.h
diff --git a/runtime/bin/dartutils.h b/runtime/bin/dartutils.h
index 9b04bfe14e7852b2e18fdb637c1ea8af0b40c216..509e16f91c25bd13e69658691625e28ef5fc6558 100644
--- a/runtime/bin/dartutils.h
+++ b/runtime/bin/dartutils.h
@@ -78,6 +78,8 @@ class DartUtils {
                                 Dart_Handle url,
                                 Dart_LibraryTag tag,
                                 const char* filename);
+  static bool PostNull(Dart_Port port_id);
+  static bool PostInteger(Dart_Port port_id, intptr_t value);
 
   static const char* kDartScheme;
   static const char* kBuiltinLibURL;