[LayoutNG] Introduce block child iterator.

third_party/WebKit/Source/core/layout/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("layout") {
   split_count = 5
 
   sources = [
@@ skipping 268 matching lines @@
     "line/LineWidth.h",
     "line/RootInlineBox.cpp",
     "line/TrailingObjects.cpp",
     "line/TrailingObjects.h",
     "ng/layout_ng_block_flow.cc",
     "ng/layout_ng_block_flow.h",
     "ng/ng_absolute_utils.cc",
     "ng/ng_absolute_utils.h",
     "ng/ng_bidi_paragraph.cc",
     "ng/ng_bidi_paragraph.h",
+    "ng/ng_block_break_token.cc",
+    "ng/ng_block_break_token.h",
+    "ng/ng_block_child_iterator.cc",
+    "ng/ng_block_child_iterator.h",
     "ng/ng_block_layout_algorithm.cc",
     "ng/ng_block_layout_algorithm.h",
     "ng/ng_block_node.cc",
     "ng/ng_block_node.h",
     "ng/ng_box_fragment.cc",
     "ng/ng_box_fragment.h",
     "ng/ng_break_token.h",
     "ng/ng_constraint_space.cc",
     "ng/ng_constraint_space.h",
     "ng/ng_constraint_space_builder.cc",
@@ skipping 76 matching lines @@
       "LayoutThemeAndroid.cpp",
       "LayoutThemeAndroid.h",
     ]
   }
 
   configs += [
     # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
     "//build/config/compiler:no_size_t_to_int_warning",
   ]
 }