[System-Keyboard-Lock] Add KeyboardLockHost and KeyEventInterceptor

components/keyboard_lock/key_event_interceptor.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_INTERCEPTOR_H_
+#define COMPONENTS_KEYBOARD_LOCK_KEY_EVENT_INTERCEPTOR_H_
+
+#include "ui/events/keycodes/keyboard_codes.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 a unpredictable thread.
+class KeyEventInterceptor {

[Wez, 2017/04/28 00:22:44]

"interceptor" sounds like this is the thing that intercepts, whereas it is
actually the thing that receives the intercepted events, I think?

Consider calling this KeyLockReceiver, or KeyLockClient (which would fit the
KeyboardLockHost naming better).

[Hzj_jie, 2017/04/28 20:02:03]

Yes, it does intercept the events, it controls whether the event should be
deprecated by returning true / false from its OnKeyDown() and OnKeyUp()
functions.

+ public:
+  KeyEventInterceptor() = default;
+  virtual ~KeyEventInterceptor() = default;
+
+  virtual bool OnKeyDown(ui::KeyboardCode code) = 0;
+  virtual bool OnKeyUp(ui::KeyboardCode code) = 0;

[Wez, 2017/04/28 00:22:44]

ui::KeyboardCode is evil and deprecated. :P

Is it possible to pass a ui::NativeEvent, or even a ui::KeyEvent here instead?

[Hzj_jie, 2017/04/28 20:02:03]

That's too bad. I suppose there is always a replacement, is there?
ui::NativeEvent is not good for the scenario: most of the logic related to this
interface are platform independent.
ui::KeyEvent is workable, but it contains up / down information, which is
conflict with OnKeyDown() and OnKeyUp() functions: AFAICT, both Windows and Mac
OS provide key down / up events separately from low level callback.

+
+  // An interface to retrieve a KeyEventInterceptor instance. This class is used
+  // to avoid the dependency of the singleton object of KeyboardLockHost, and to
+  // ensure late installed KeyEventInterceptor can be retrieved.
+  class Retriever {
+   public:
+    Retriever() = default;
+    virtual ~Retriever() = default;
+
+    // May return nullptr.
+    virtual KeyEventInterceptor* Get() = 0;
+  };
+};
+
+}  // namespace keyboard_lock
+
+#endif  // COMPONENTS_KEYBOARD_LOCK_KEY_EVENT_INTERCEPTOR_H_