2nd attempt at adding streamListen/streamCancel to the service protocol.

runtime/vm/json_stream.h

 // Copyright (c) 2013, 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_JSON_STREAM_H_
 #define VM_JSON_STREAM_H_
 
 #include "include/dart_api.h"  // for Dart_Port
 #include "platform/json.h"
 #include "vm/allocation.h"
@@ skipping 10 matching lines @@
 class MessageQueue;
 class Metric;
 class Object;
 class Script;
 class ServiceEvent;
 class Breakpoint;
 class String;
 class Zone;
 
 
-// Keep this in sync with runtime/observatory/lib/src/service/object.dart.
+// Keep this enum in sync with:
+//
+//  - runtime/vm/service/vmservice.dart
+//  - runtime/observatory/lib/src/service/object.dart
+//
 enum JSONRpcErrorCode {
   kParseError     = -32700,
   kInvalidRequest = -32600,
   kMethodNotFound = -32601,
   kInvalidParams  = -32602,
   kInternalError  = -32603,
 
-  kFeatureDisabled     = 100,
-  kVMMustBePaused      = 101,
-  kCannotAddBreakpoint = 102,
+  kFeatureDisabled         = 100,
+  kVMMustBePaused          = 101,
+  kCannotAddBreakpoint     = 102,
+  kStreamAlreadySubscribed = 103,
+  kStreamNotSubscribed     = 104,
 };
 
 
 class JSONStream : ValueObject {
  public:
   explicit JSONStream(intptr_t buf_size = 256);
   ~JSONStream();
 
   void Setup(Zone* zone,
              Dart_Port reply_port,
@@ skipping 238 matching lines @@
 
   friend class JSONObject;
 
   DISALLOW_ALLOCATION();
   DISALLOW_COPY_AND_ASSIGN(JSONArray);
 };
 
 }  // namespace dart
 
 #endif  // VM_JSON_STREAM_H_