performance measurement improvements and README update

pkg/analysis_server/benchmark/integration/operation.dart

Index: pkg/analysis_server/benchmark/integration/operation.dart
diff --git a/pkg/analysis_server/benchmark/integration/operation.dart b/pkg/analysis_server/benchmark/integration/operation.dart
index 5816a9ed3e3ac7282524846d0fb17440dd5ab075..9e408d8cbba77fd57bbab6c0264fff97ac75d238 100644
--- a/pkg/analysis_server/benchmark/integration/operation.dart
+++ b/pkg/analysis_server/benchmark/integration/operation.dart
@@ -111,7 +111,7 @@ class RequestOperation extends Operation {
  * A [ResponseOperation] waits for a [JSON] response from the server.
  */
 class ResponseOperation extends Operation {
-  static final Duration responseTimeout = new Duration(seconds: 5);
+  static final Duration responseTimeout = new Duration(seconds: 60);
   final CommonInputConverter converter;
   final Map<String, dynamic> requestJson;
   final Map<String, dynamic> responseJson;