Initial UserTag and dart:profiler library

tests/lib/profiler/user_tags_test.dart

Index: tests/lib/profiler/user_tags_test.dart
diff --git a/tests/lib/profiler/user_tags_test.dart b/tests/lib/profiler/user_tags_test.dart
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+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+//
+
+import 'dart:profiler';
+import 'package:expect/expect.dart';
+
+// Test that the label property matches the constructor.
+void testLabel() {
+  var label = 'Hello World';
+  var tag = new UserTag(label);
+  Expect.equals(label, tag.label);
+}
+
+
+// Test that we canonicalize UserTag by name.
+void testCanonicalize(tag1) {
+  var label = 'Global Tag';
+  var tag = new UserTag(label);
+  Expect.isTrue(identical(tag, tag1));
+}
+
+
+// Test that we made the tag current.
+void testMakeCurrent(tag) {
+  tag.makeCurrent();
+  Expect.isTrue(identical(tag, getCurrentTag()));
+}
+
+
+// Test clearCurrentTag.
+void testClearCurrent(tag) {
+  tag.makeCurrent();
+  Expect.isTrue(identical(tag, getCurrentTag()));
+  var old_tag = clearCurrentTag();
+  Expect.isTrue(identical(tag, old_tag));
+  Expect.isNull(getCurrentTag());
+}
+
+
+// Test that we reach a limit of tags an exception is thrown.
+void testExhaust() {
+  var i = 0;
+  while (true) {
+    var label = i.toString();
+    var tag = new UserTag(label);
+    i++;
+  }
+}
+
+
+main() {
+  var label = 'Global Tag';
+  var tag = new UserTag(label);
+  testLabel();
+  testCanonicalize(tag);
+  for (var i = 0; i < 2000; i++) {
+    testMakeCurrent(tag);
+  }
+  testClearCurrent(tag);
+  Expect.throws(testExhaust);
+}