pkg/unittest: Run each test in a Zone

pkg/unittest/lib/src/spread_args_helper.dart

Index: pkg/unittest/lib/src/spread_args_helper.dart
diff --git a/pkg/unittest/lib/src/spread_args_helper.dart b/pkg/unittest/lib/src/spread_args_helper.dart
index 08dd45868ee6b3a1da9fbabcaa76c83378ead782..41411b93780f4f2d68f4f6941dad6186b668f4f4 100644
--- a/pkg/unittest/lib/src/spread_args_helper.dart
+++ b/pkg/unittest/lib/src/spread_args_helper.dart
@@ -12,7 +12,6 @@ class _SpreadArgsHelper {
   int actualCalls = 0;
   final TestCase testCase;
   bool complete;
-  static const sentinel = const _Sentinel();
 
   _SpreadArgsHelper(Function callback, int minExpected, int maxExpected,
       Function isDone, String id)
@@ -120,4 +119,15 @@ class _SpreadArgsHelper {
         },
         after, testCase);
   }
+
+  _guardAsync(Function tryBody, Function finallyBody, TestCase testCase) {
+    assert(testCase != null);
+    try {
+      return tryBody();
+    } catch (e, trace) {
+      _registerException(testCase, e, trace);
+    } finally {
+      if (finallyBody != null) finallyBody();
+    }
+  }
 }