- Add a minimal implementation of Capability.

runtime/vm/message.h

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_MESSAGE_H_
 #define VM_MESSAGE_H_
 
 #include "vm/thread.h"
 
 // Duplicated from dart_api.h to avoid including the whole header.
@@ skipping 16 matching lines @@
   static const Dart_Port kIllegalPort = 0;
 
   // A new message to be sent between two isolates. The data handed to this
   // message will be disposed by calling free() once the message object is
   // being destructed (after delivery or when the receiving port is closed).
   Message(Dart_Port dest_port, uint8_t* data, intptr_t len, Priority priority)
       : next_(NULL),
         dest_port_(dest_port),
         data_(data),
         len_(len),
-        priority_(priority) {}
+        priority_(priority) {
+    ASSERT(dest_port != kIllegalPort);
+  }
   ~Message() {
     free(data_);
   }
 
   Dart_Port dest_port() const { return dest_port_; }
   uint8_t* data() const { return data_; }
   intptr_t len() const { return len_; }
   Priority priority() const { return priority_; }
 
   bool IsOOB() const { return priority_ == Message::kOOBPriority; }
@@ skipping 30 matching lines @@
 
   Message* head_;
   Message* tail_;
 
   DISALLOW_COPY_AND_ASSIGN(MessageQueue);
 };
 
 }  // namespace dart
 
 #endif  // VM_MESSAGE_H_