Update from https://crrev.com/308331

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")
 
 if (is_android) {
   import("//build/config/android/rules.gni")
 }
 
@@ skipping 103 matching lines @@
     "build_time.cc",
     "build_time.h",
     "callback.h",
     "callback_helpers.cc",
     "callback_helpers.h",
     "callback_internal.cc",
     "callback_internal.h",
     "cancelable_callback.h",
     "command_line.cc",
     "command_line.h",
+    "chromeos/memory_pressure_observer_chromeos.cc",
+    "chromeos/memory_pressure_observer_chromeos.h",
     "compiler_specific.h",
     "containers/adapters.h",
     "containers/hash_tables.h",
     "containers/linked_list.h",
     "containers/mru_cache.h",
     "containers/small_map.h",
     "containers/stack_container.h",
     "cpu.cc",
     "cpu.h",
     "critical_closure.h",
@@ skipping 108 matching lines @@
     "guid_win.cc",
     "hash.cc",
     "hash.h",
     "id_map.h",
     "ios/device_util.h",
     "ios/device_util.mm",
     "ios/ios_util.h",
     "ios/ios_util.mm",
     "ios/scoped_critical_action.h",
     "ios/scoped_critical_action.mm",
+    "ios/weak_nsobject.h",
+    "ios/weak_nsobject.mm",
     "json/json_file_value_serializer.cc",
     "json/json_file_value_serializer.h",
     "json/json_parser.cc",
     "json/json_parser.h",
     "json/json_reader.cc",
     "json/json_reader.h",
     "json/json_string_value_serializer.cc",
     "json/json_string_value_serializer.h",
     "json/json_value_converter.h",
     "json/json_writer.cc",
@@ skipping 502 matching lines @@
   defines = [ "BASE_IMPLEMENTATION" ]
 
   deps = [
     ":base_static",
     "//base/allocator:allocator_extension_thunks",
     "//base/third_party/dynamic_annotations",
     "//base/third_party/nspr",
     "//third_party/modp_b64",
   ]
 
+  # Allow more direct string conversions on platforms with native utf8
+  # strings
+  if (is_mac || is_ios || is_chromeos) {
+    defines += [ "SYSTEM_NATIVE_UTF8" ]
+  }
+
   if (is_android) {
     sources += [
       "memory/discardable_memory_ashmem_allocator.cc",
       "memory/discardable_memory_ashmem_allocator.h",
       "memory/discardable_memory_ashmem.cc",
       "memory/discardable_memory_ashmem.h",
     ]
     sources -= [
       "base_paths_posix.cc",
       "power_monitor/power_monitor_device_source_posix.cc",
@@ skipping 396 matching lines @@
     "i18n/case_conversion_unittest.cc",
     "i18n/file_util_icu_unittest.cc",
     "i18n/icu_string_conversions_unittest.cc",
     "i18n/number_formatting_unittest.cc",
     "i18n/rtl_unittest.cc",
     "i18n/streaming_utf8_validator_unittest.cc",
     "i18n/string_search_unittest.cc",
     "i18n/time_formatting_unittest.cc",
     "i18n/timezone_unittest.cc",
     "ios/device_util_unittest.mm",
+    "ios/weak_nsobject_unittest.mm",
     "json/json_parser_unittest.cc",
     "json/json_reader_unittest.cc",
     "json/json_value_converter_unittest.cc",
     "json/json_value_serializer_unittest.cc",
     "json/json_writer_unittest.cc",
     "json/string_escape_unittest.cc",
     "lazy_instance_unittest.cc",
     "logging_unittest.cc",
     "mac/bind_objc_block_unittest.mm",
     "mac/foundation_util_unittest.mm",
@@ skipping 317 matching lines @@
   # GYP: //base.gyp:base_unittests_apk
   unittest_apk("base_unittests_apk") {
     deps = [
       ":base_java",
       ":base_java_unittest_support",
       ":base_unittests",
     ]
     unittests_dep = ":base_unittests"
   }
 }