Add trace_service_pause_events flag and related tracing

tests/standalone/vmservice/test_helper.dart

Index: tests/standalone/vmservice/test_helper.dart
diff --git a/tests/standalone/vmservice/test_helper.dart b/tests/standalone/vmservice/test_helper.dart
index d7c580ec05e4d0f11a998f68117119d3a8eadf15..fde93e047f96ddf31426e2b5aad30dd9d07c1fd9 100644
--- a/tests/standalone/vmservice/test_helper.dart
+++ b/tests/standalone/vmservice/test_helper.dart
@@ -140,7 +140,7 @@ class TestLauncher {
       var first = true;
       process.stdout.transform(UTF8.decoder)
                     .transform(new LineSplitter()).listen((line) {
-        if (line.startsWith('VMService listening on ')) {
+        if (line.startsWith('Observatory listening on http://')) {
           RegExp portExp = new RegExp(r"\d+.\d+.\d+.\d+:(\d+)");
           var port = portExp.firstMatch(line).group(1);
           portNumber = int.parse(port);