[System-Keyboard-Lock] Add KeyboardLockHost and KeyEventInterceptor

components/keyboard_lock/key_event_filter.h

+// Copyright 2017 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_KEYBOARD_LOCK_KEY_EVENT_FILTER_H_
+#define COMPONENTS_KEYBOARD_LOCK_KEY_EVENT_FILTER_H_
+
+#include "components/keyboard_lock/keyboard_lock_types.h"
+
+namespace keyboard_lock {
+
+// An interface to receive and process a key event. The implementation needs to
+// guarantee the thread-safety of OnKeyDown() and OnKeyUp() functions, which may
+// be executed in an unpredictable thread.
+class KeyEventFilter {
+ public:
+  KeyEventFilter() = default;
+  virtual ~KeyEventFilter() = default;
+
+  // Returns true if the |code| should be suppressed.
+  virtual bool OnKeyDown(NativeKeycode code) = 0;
+
+  // REturns true if the |code| should be suppressed.
+  virtual bool OnKeyUp(NativeKeycode code) = 0;
+};
+
+}  // namespace keyboard_lock
+
+#endif  // COMPONENTS_KEYBOARD_LOCK_KEY_EVENT_FILTER_H_