[System-Keyboard-Lock] Add KeyboardLockHost and KeyEventInterceptor

components/keyboard_lock/key_event_interceptor_installer.cc

+// 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.
+
+#include "components/keyboard_lock/key_event_interceptor_installer.h"
+
+#include <memory>
+
+#include "base/logging.h"
+#include "components/keyboard_lock/keyboard_lock_host.h"
+
+namespace keyboard_lock {
+
+KeyEventInterceptorInstaller::KeyEventInterceptorInstaller(
+    KeyboardLockHost* host) {
+  DCHECK(host);
+  host->SetKeyEventInterceptor(std::unique_ptr<KeyEventInterceptor>(this));

[dtapuska, 2017/04/18 13:43:17]

I'd think this is dangerous. What happens if the SetKeyEventInterceptor calls
the virtual methods during the set? I personally prefer construction and
registration to be separate. You could have a static method that Creates and
Registers an instance but it isn't actually the ctor.

[Hzj_jie, 2017/04/19 00:46:26]

Done.
Good point, I have not considered this possibility before: the
SetKeyEventInterceptor() does not likely call any functions of
KeyEventInterceptor.

+}
+
+KeyEventInterceptorInstaller::~KeyEventInterceptorInstaller() = default;
+
+}  // namespace keyboard_lock