[LayoutNG] Introduce block child iterator.

third_party/WebKit/Source/core/layout/ng/ng_block_break_token.cc

+// 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.
+
+#include "core/layout/ng/ng_block_break_token.h"
+
+#include "core/layout/ng/ng_block_node.h"
+
+namespace blink {
+
+NGBlockBreakToken::NGBlockBreakToken(
+    NGBlockNode* node,
+    LayoutUnit used_block_size,
+    HeapVector<Member<NGBreakToken>>& child_break_tokens)
+    : NGBreakToken(kBlockBreakToken, kUnfinished, node),
+      used_block_size_(used_block_size) {
+  child_break_tokens_.swap(child_break_tokens);
+}
+
+NGBlockBreakToken::NGBlockBreakToken(NGBlockNode* node)
+    : NGBreakToken(kBlockBreakToken, kFinished, node) {}
+
+NGBlockBreakToken::NGBlockBreakToken(NGBlockNode* node, LayoutUnit break_offset)
+    : NGBreakToken(kBlockBreakToken, kUnfinished, node),
+      break_offset_(break_offset) {}
+
+}  // namespace blink