mus: Add EventObserver to allow passively listening to UI events

components/mus/public/cpp/event_matcher.h

Index: components/mus/public/cpp/event_matcher.h
diff --git a/components/mus/public/cpp/event_matcher.h b/components/mus/public/cpp/event_matcher.h
deleted file mode 100644
index d6e25cbe63b9ae68f5aacb79bda7a51343eb94d3..0000000000000000000000000000000000000000
--- a/components/mus/public/cpp/event_matcher.h
+++ /dev/null
@@ -1,20 +0,0 @@
-// 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 COMPONENTS_MUS_PUBLIC_CPP_EVENT_MATCHER_H_
-#define COMPONENTS_MUS_PUBLIC_CPP_EVENT_MATCHER_H_
-
-#include "components/mus/public/interfaces/input_event_constants.mojom.h"
-#include "components/mus/public/interfaces/input_event_matcher.mojom.h"
-#include "components/mus/public/interfaces/input_key_codes.mojom.h"
-
-namespace mus {
-
-// |flags| is a bitfield of kEventFlag* and kMouseEventFlag* values in
-// input_event_constants.mojom.
-mojom::EventMatcherPtr CreateKeyMatcher(mojom::KeyboardCode code, int flags);
-
-}  // namespace mus
-
-#endif  // COMPONENTS_MUS_PUBLIC_CPP_EVENT_MATCHER_H_