Allow analysis server integration tests to run without package root.

pkg/analysis_server/test/integration/integration_tests.dart

Index: pkg/analysis_server/test/integration/integration_tests.dart
diff --git a/pkg/analysis_server/test/integration/integration_tests.dart b/pkg/analysis_server/test/integration/integration_tests.dart
index a565119025715492857fc9af435e0aa7871a7721..10dc563717fa992ef35660e970038441c88f7b82 100644
--- a/pkg/analysis_server/test/integration/integration_tests.dart
+++ b/pkg/analysis_server/test/integration/integration_tests.dart
@@ -516,7 +516,9 @@ class Server {
     if (debugServer) {
       arguments.add('--debug');
     }
-    arguments.add('--package-root=${Platform.packageRoot}');
+    if (Platform.packageRoot.isNotEmpty) {
+      arguments.add('--package-root=${Platform.packageRoot}');
+    }
     arguments.add(serverPath);
     return Process.start(dartBinary, arguments).then((Process process) {
       Server server = new Server._(process);