pkg/unittest: GroupContext should be private

pkg/unittest/lib/unittest.dart

Index: pkg/unittest/lib/unittest.dart
diff --git a/pkg/unittest/lib/unittest.dart b/pkg/unittest/lib/unittest.dart
index b2abf06978991122605c7f5a6cdab8c041606307..032b4d51eeda19c1488a6b3e4bc23a9006c6e446 100644
--- a/pkg/unittest/lib/unittest.dart
+++ b/pkg/unittest/lib/unittest.dart
@@ -217,8 +217,8 @@ final List<TestCase> testCases = new UnmodifiableListView<TestCase>(_testCases);
  * Setup and teardown functions for a group and its parents, the latter
  * for chaining.
  */
-class GroupContext {
-  final GroupContext parent;
+class _GroupContext {
+  final _GroupContext parent;
 
   /** Description text of the current test group. */
   final String _name;
@@ -273,7 +273,7 @@ class GroupContext {
       ? _name
       : "${parent.fullName}$groupSep$_name";
 
-  GroupContext([this.parent, this._name = '']) {
+  _GroupContext([this.parent, this._name = '']) {
     _testSetup = parentSetup;
     _testTeardown = parentTeardown;
   }
@@ -282,8 +282,8 @@ class GroupContext {
 // We use a 'dummy' context for the top level to eliminate null
 // checks when querying the context. This allows us to easily
 //  support top-level setUp/tearDown functions as well.
-GroupContext _rootContext = new GroupContext();
-GroupContext _currentContext = _rootContext;
+final _rootContext = new _GroupContext();
+_GroupContext _currentContext = _rootContext;
 
 int _currentTestCaseIndex = 0;
 
@@ -583,7 +583,7 @@ Function protectAsync2(Function callback, {String id}) {
  */
 void group(String description, void body()) {
   ensureInitialized();
-  _currentContext = new GroupContext(_currentContext, description);
+  _currentContext = new _GroupContext(_currentContext, description);
   try {
     body();
   } catch (e, trace) {