Always capture stack traces when running pub tests.

sdk/lib/_internal/pub/test/test_pub.dart

Index: sdk/lib/_internal/pub/test/test_pub.dart
diff --git a/sdk/lib/_internal/pub/test/test_pub.dart b/sdk/lib/_internal/pub/test/test_pub.dart
index b978d54bfa017c586ab4a03e3547c50a0f025325..dbc326c3608ac083f30b13f8ce8dc038aea0f7fa 100644
--- a/sdk/lib/_internal/pub/test/test_pub.dart
+++ b/sdk/lib/_internal/pub/test/test_pub.dart
@@ -250,11 +250,6 @@ void _integration(String description, void body(), [Function testFn]) {
       currentSchedule.timeout = new Duration(seconds: 10);
     }
 
-    // By default, don't capture stack traces since they slow the tests way
-    // down. To debug failing tests, comment this out.
-    currentSchedule.captureStackTraces =
-        new Options().arguments.contains('--trace');
-
     // Ensure the SDK version is always available.
     d.dir(sdkPath, [
       d.file('version', '0.1.2.3')