[System-Keyboard-Lock] Add KeyboardLockHost and KeyEventInterceptor

components/keyboard_lock/keyboard_lock_host.h

Index: components/keyboard_lock/keyboard_lock_host.h
diff --git a/components/keyboard_lock/keyboard_lock_host.h b/components/keyboard_lock/keyboard_lock_host.h
new file mode 100644
index 0000000000000000000000000000000000000000..cd1092d6d86413f1843933955ae656454bd0a59b
--- /dev/null
+++ b/components/keyboard_lock/keyboard_lock_host.h
@@ -0,0 +1,66 @@
+// 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_KEYBOARD_LOCK_HOST_H_
+#define COMPONENTS_KEYBOARD_LOCK_KEYBOARD_LOCK_HOST_H_
+
+#include <memory>
+
+#include "base/gtest_prod_util.h"
+#include "base/macros.h"
+#include "base/synchronization/lock.h"
+#include "components/keyboard_lock/key_event_interceptor.h"
+
+namespace base {
+template <typename T>
+struct DefaultSingletonTraits;
+}  // namespace base
+
+namespace keyboard_lock {
+
+class KeyEventInterceptorInstaller;
+
+FORWARD_DECLARE_TEST(KeyboardLockHostTest, KeyEventInterceptorInstallationTest);
+
+class KeyboardLockHost final {
+ public:
+  static KeyboardLockHost* GetInstance();
+
+  ~KeyboardLockHost();
+
+  // May return nullptr if not interceptor has been installed. This function
+  // never returns a destroyed object: only one KeyEventInterceptor installation
+  // is allowed during the lifetime of the process.
+  KeyEventInterceptor* interceptor();
+
+  std::unique_ptr<KeyEventInterceptor::Retriever> GetInterceptorRetriever();
+
+ private:
+  // Allows KeyEventInterceptorInstaller to access SetKeyEventInterceptor().
+  friend class KeyEventInterceptorInstaller;
+
+  // Allows Singleton to create a instance of KeyboardLockHost.
+  friend struct base::DefaultSingletonTraits<KeyboardLockHost>;
+
+  // Allows test cases to create a new instance of KeyboardLockHost.
+  FRIEND_TEST_ALL_PREFIXES(KeyboardLockHostTest,
+                           KeyEventInterceptorInstallationTest);
+
+  KeyboardLockHost();
+
+  void SetKeyEventInterceptor(std::unique_ptr<KeyEventInterceptor> interceptor);
+
+  // GUARDED_BY(lock_)
+  std::unique_ptr<KeyEventInterceptor> interceptor_;
+
+  // This lock only guards |interceptor_|, other function calls should be
+  // forwarded to UI thread.
+  mutable base::Lock lock_;
+
+  DISALLOW_COPY_AND_ASSIGN(KeyboardLockHost);
+};
+
+}  // namespace keyboard_lock
+
+#endif  // COMPONENTS_KEYBOARD_LOCK_KEYBOARD_LOCK_HOST_H_