Introduced support for external services registration in the ServiceProtocol

sdk/lib/vmservice/named_lookup.dart

Index: sdk/lib/vmservice/named_lookup.dart
diff --git a/sdk/lib/vmservice/named_lookup.dart b/sdk/lib/vmservice/named_lookup.dart
new file mode 100644
index 0000000000000000000000000000000000000000..dd9ce9e04cc4696935a23331052ae1a499bf4979
--- /dev/null
+++ b/sdk/lib/vmservice/named_lookup.dart
@@ -0,0 +1,59 @@
+// Copyright (c) 2017, 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.
+
+part of dart._vmservice;
+
+class NamedLookup<E> extends Object with IterableMixin<E> {
+  final IdGenerator _generator;
+  final Map<String, E> _elements = new Map<String, E>();
+  final Map<E, String> _ids = new Map<E, String>();
+
+  NamedLookup({String prologue = ''})
+      : super(),
+        _generator = new IdGenerator(prologue: prologue);
+
+  void add(E e) {
+    final id = _generator.newId();
+    _elements[id] = e;
+    _ids[e] = id;
+  }
+
+  void remove(E e) {
+    final id = _ids.remove(e);
+    _elements.remove(id);
+    _generator.release(id);
+  }
+
+  E operator [](String id) => _elements[id];
+  String keyOf(E e) => _ids[e];
+
+  Iterator<E> get iterator => _ids.keys.iterator;
+}
+
+class IdGenerator {
+  final String prologue;
+  final Set<String> _used = new Set<String>();
+  final Set<String> _free = new Set<String>();
+  int _next = 0;
+
+  IdGenerator({this.prologue = ''});
+
+  String newId() {
+    var id;
+    if (_free.isEmpty) {
+      id = prologue + (_next++).toString();
+    } else {
+      id = _free.first;
+    }
+    _free.remove(id);
+    _used.add(id);
+    return id;
+  }
+
+  void release(String id) {
+    if (_used.remove(id)) {
+      _free.add(id);
+    }
+  }
+}