Add quotes to make it easier to copy paste around.

tools/testing/dart/test_suite.dart

Index: tools/testing/dart/test_suite.dart
diff --git a/tools/testing/dart/test_suite.dart b/tools/testing/dart/test_suite.dart
index 2a6fa1858d5c12133994fdb7c825d92f2323a007..990e7ab144ec0a0ebf3dca68459d9689c1669f6e 100644
--- a/tools/testing/dart/test_suite.dart
+++ b/tools/testing/dart/test_suite.dart
@@ -1181,8 +1181,9 @@ class StandardTestSuite extends TestSuite {
       return configuration['drt'];
     }
     if (Platform.operatingSystem == 'macos') {
-      return dartDir.append('/client/tests/drt/Content Shell.app/Contents/'
-                            'MacOS/Content Shell').toNativePath();
+      final path = dartDir.append(
+          '/client/tests/drt/Content Shell.app/Contents/MacOS/Content Shell');
+      return '"${path.toNativePath()}"';
     }
     return dartDir.append('client/tests/drt/content_shell').toNativePath();
   }