Add DocumentShutdown{Notifier,Observer}

third_party/WebKit/Source/core/dom/BUILD.gn

 # Copyright 2016 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("//third_party/WebKit/Source/core/core.gni")
 
 blink_core_sources("dom") {
   split_count = 5
 
   sources = [
@@ skipping 106 matching lines @@
     "DocumentOrShadowRoot.h",
     "DocumentOrderedList.cpp",
     "DocumentOrderedList.h",
     "DocumentOrderedMap.cpp",
     "DocumentOrderedMap.h",
     "DocumentParser.cpp",
     "DocumentParser.h",
     "DocumentParserClient.h",
     "DocumentParserTiming.cpp",
     "DocumentParserTiming.h",
+    "DocumentShutdownNotifier.cpp",
+    "DocumentShutdownNotifier.h",
+    "DocumentShutdownObserver.cpp",
+    "DocumentShutdownObserver.h",
     "DocumentStatisticsCollector.cpp",
     "DocumentStatisticsCollector.h",
     "DocumentStyleSheetCollection.cpp",
     "DocumentStyleSheetCollection.h",
     "DocumentStyleSheetCollector.cpp",
     "DocumentStyleSheetCollector.h",
     "DocumentTiming.cpp",
     "DocumentTiming.h",
     "DocumentType.cpp",
     "DocumentType.h",
@@ skipping 314 matching lines @@
     "shadow/SlotAssignment.h",
     "shadow/SlotScopedTraversal.cpp",
     "shadow/SlotScopedTraversal.h",
   ]
 
   configs += [
     # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
     "//build/config/compiler:no_size_t_to_int_warning",
   ]
 }