Implement utility-side host resolver Mojo client.

net/test/event_waiter.h

+// 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 NET_TEST_EVENT_WAITER_H_
+#define NET_TEST_EVENT_WAITER_H_
+
+#include "base/run_loop.h"
+
+namespace net {
+
+// Helper class to run a RunLoop until an expected event is reported.
+template <typename Event>
+class EventWaiter {
+ public:
+  // Runs a RunLoop until NotifyEvent() is called with |event|.
+  void WaitForEvent(Event event) {
+    expected_event_ = event;
+    base::RunLoop run_loop;
+    quit_closure_ = run_loop.QuitClosure();
+    run_loop.Run();
+  }
+
+  // Unblocks a WaitForEvent() call if it was called with |event|. Otherwise,
+  // has no effect.
+  void NotifyEvent(Event event) {
+    if (event == expected_event_ && !quit_closure_.is_null()) {
+      quit_closure_.Run();
+      quit_closure_.Reset();
+    }
+  }
+
+ private:
+  Event expected_event_;
+  base::Closure quit_closure_;
+};
+
+}  // namespace net
+
+#endif  // NET_TEST_EVENT_WAITER_H_