[System-Keyboard-Lock] Add KeyboardLockHost and KeyEventInterceptor

components/keyboard_lock/BUILD.gn

+# 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.
+
+static_library("keyboard_lock") {
+  sources = [
+    "key_event_interceptor.h",
+    "key_event_interceptor_installer.cc",
+    "key_event_interceptor_installer.h",
+    "keyboard_lock_host.cc",
+    "keyboard_lock_host.h",
+  ]
+
+  deps = [
+    "//base",
+    "//ui/events:event_constants",
+  ]
+}
+
+source_set("unit_tests") {
+  testonly = true
+  sources = [
+    "keyboard_lock_host_unittest.cc",
+  ]
+
+  deps = [
+    ":keyboard_lock",
+    "//testing/gtest",
+  ]
+}