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/base/utils.dart

diff --git a/packages/flutter_tools/lib/src/base/utils.dart b/packages/flutter_tools/lib/src/base/utils.dart
index a550f9c..312739a 100644
--- a/packages/flutter_tools/lib/src/base/utils.dart
+++ b/packages/flutter_tools/lib/src/base/utils.dart
@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 import 'dart:async';
+import 'dart:convert';
 import 'dart:io';
 
 import 'package:crypto/crypto.dart';
@@ -60,6 +61,10 @@
   }
 }
 
+String toPrettyJson(Object jsonable) {
+  return new JsonEncoder.withIndent('  ').convert(jsonable) + '\n';
+}
+
 /// A class to maintain a list of items, fire events when items are added or
 /// removed, and calculate a diff of changes when a new list of items is
 /// available.