Added test support to observe and verify UMA user actions during tests.

base/test/user_action_tester.h

Index: base/test/user_action_tester.h
diff --git a/base/test/user_action_tester.h b/base/test/user_action_tester.h
new file mode 100644
index 0000000000000000000000000000000000000000..6e9f1919b4014039ba4b136068a6b07b8949964a
--- /dev/null
+++ b/base/test/user_action_tester.h
@@ -0,0 +1,45 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_TEST_USER_ACTION_TESTER_H_
+#define BASE_TEST_USER_ACTION_TESTER_H_
+
+#include <map>
+#include <string>
+
+#include "base/metrics/user_metrics.h"
+
+namespace base {
+
+// This class observes and collects user action notifications that are sent
+// by the tests, so that they can be examined afterwards for correctness.

[Mark Mentovai, 2015/04/13 17:30:00]

Is this thread-safe? Does it need to be?

[bruthig, 2015/04/13 19:21:46]

Updated documentation.

There isn't currently a use case that requires this to be thread-safe.

+class UserActionTester {
+ public:
+  UserActionTester();
+  ~UserActionTester();
+
+  // Returns the number of times the given |user_action| occurred.
+  int GetActionCount(const std::string& user_action) const;
+
+  // Resets all user action counts to 0.
+  void ResetCounts();
+
+ private:
+  typedef std::map<std::string, int> UserActionCountMap;
+
+  // The callback that is notified when a user actions occurs.
+  void OnUserAction(const std::string& user_action);
+
+  // A map that tracks the number of times a user action has occurred.
+  UserActionCountMap count_map_;
+
+  // The callback that is added to the global action callback list.
+  base::ActionCallback action_callback_;
+
+  DISALLOW_COPY_AND_ASSIGN(UserActionTester);
+};
+
+}  // namespace base
+
+#endif  // BASE_TEST_USER_ACTION_TESTER_H_