Base: add Optional<T>.

base/BUILD.gn

 # Copyright (c) 2013 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.
 
 import("//build/config/ui.gni")
 import("//testing/test.gni")
 
 if (is_android) {
   import("//build/config/android/rules.gni")
 }
@@ skipping 340 matching lines @@
     "nix/mime_util_xdg.cc",
     "nix/mime_util_xdg.h",
     "nix/xdg_util.cc",
     "nix/xdg_util.h",
     "numerics/safe_conversions.h",
     "numerics/safe_conversions_impl.h",
     "numerics/safe_math.h",
     "numerics/safe_math_impl.h",
     "observer_list.h",
     "observer_list_threadsafe.h",
+    "optional.h",
     "os_compat_android.cc",
     "os_compat_android.h",
     "os_compat_nacl.cc",
     "os_compat_nacl.h",
     "path_service.cc",
     "path_service.h",
     "pending_task.cc",
     "pending_task.h",
     "pickle.cc",
     "pickle.h",
@@ skipping 944 matching lines @@
     "metrics/histogram_macros_unittest.cc",
     "metrics/histogram_snapshot_manager_unittest.cc",
     "metrics/histogram_unittest.cc",
     "metrics/sample_map_unittest.cc",
     "metrics/sample_vector_unittest.cc",
     "metrics/sparse_histogram_unittest.cc",
     "metrics/statistics_recorder_unittest.cc",
     "move_unittest.cc",
     "numerics/safe_numerics_unittest.cc",
     "observer_list_unittest.cc",
+    "optional_unittest.cc",
     "os_compat_android_unittest.cc",
     "path_service_unittest.cc",
     "pickle_unittest.cc",
     "posix/file_descriptor_shuffle_unittest.cc",
     "posix/unix_domain_socket_linux_unittest.cc",
     "power_monitor/power_monitor_unittest.cc",
     "prefs/default_pref_store_unittest.cc",
     "prefs/json_pref_store_unittest.cc",
     "prefs/overlay_user_pref_store_unittest.cc",
     "prefs/pref_change_registrar_unittest.cc",
@@ skipping 320 matching lines @@
 
   # GYP: //base.gyp:base_java_unittest_support
   android_library("base_java_unittest_support") {
     deps = [
       ":base_java",
     ]
     java_files =
         [ "test/android/java/src/org/chromium/base/ContentUriTestUtils.java" ]
   }
 }