Consolidate observatory code (#3892)

* rename service_protocol.dart to protocol_discovery.dart

* add a wrapper around the obs. protocol

* use json-rpc in run

* consolidate obs. code; implement flutter run --benchmark

* review comments

packages/flutter_tools/lib/src/protocol_discovery.dart

diff --git a/packages/flutter_tools/lib/src/protocol_discovery.dart b/packages/flutter_tools/lib/src/protocol_discovery.dart
new file mode 100644
index 0000000..7c27b13
--- /dev/null
+++ b/packages/flutter_tools/lib/src/protocol_discovery.dart
@@ -0,0 +1,57 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:async';
+
+import 'device.dart';
+
+/// Discover service protocol ports on devices.
+class ProtocolDiscovery {
+  /// [logReader] - a [DeviceLogReader] to look for service messages in.
+  ProtocolDiscovery(DeviceLogReader logReader, String serviceName)
+      : _logReader = logReader, _serviceName = serviceName {
+    assert(_logReader != null);
+    _subscription = _logReader.logLines.listen(_onLine);
+  }
+
+  static const String kObservatoryService = 'Observatory';
+  static const String kDiagnosticService = 'Diagnostic server';
+
+  final DeviceLogReader _logReader;
+  final String _serviceName;
+
+  Completer<int> _completer = new Completer<int>();
+  StreamSubscription<String> _subscription;
+
+  /// The [Future] returned by this function will complete when the next service
+  /// protocol port is found.
+  Future<int> nextPort() => _completer.future;
+
+  void cancel() {
+    _subscription.cancel();
+  }
+
+  void _onLine(String line) {
+    int portNumber = 0;
+    if (line.contains('$_serviceName listening on http://')) {
+      try {
+        RegExp portExp = new RegExp(r"\d+.\d+.\d+.\d+:(\d+)");
+        String port = portExp.firstMatch(line).group(1);
+        portNumber = int.parse(port);
+      } catch (_) {
+        // Ignore errors.
+      }
+    }
+    if (portNumber != 0)
+      _located(portNumber);
+  }
+
+  void _located(int port) {
+    assert(_completer != null);
+    assert(!_completer.isCompleted);
+
+    _completer.complete(port);
+    _completer = new Completer<int>();
+  }
+}