[LayoutNG] Introduce block child iterator.

third_party/WebKit/Source/core/layout/ng/ng_block_child_iterator.h

+// 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.
+
+#ifndef NGBlockChildIterator_h
+#define NGBlockChildIterator_h
+
+#include "core/CoreExport.h"
+#include "platform/heap/Handle.h"
+
+namespace blink {
+
+class NGLayoutInputNode;
+class NGBreakToken;
+class NGBlockBreakToken;
+
+// A utility class for block-flow layout which given the first child and a
+// break token will iterator through unfinished children.

[atotic, 2017/02/22 05:45:07]

s/iterator/iterate ?

As a user of iterator API, I often need to know how does iterator
behaves wrt modifications (and most of Chrome docs do not specify
this). Might want to add a note about it.

[ikilpatrick, 2017/02/22 18:47:19]

Done?

+class CORE_EXPORT NGBlockChildIterator {
+ public:
+  NGBlockChildIterator(NGLayoutInputNode* first_child,
+                       NGBlockBreakToken* break_token);
+
+  // Returns the next input node which should be laid out, along with its
+  // respective break token.
+  std::pair<NGLayoutInputNode*, NGBreakToken*> NextChild();
+
+ private:
+  Persistent<NGLayoutInputNode> child_;
+  Persistent<NGBlockBreakToken> break_token_;
+
+  size_t child_token_idx_;

[mstensho (USE GERRIT), 2017/02/22 13:11:31]

Please document what this is.

[ikilpatrick, 2017/02/22 18:47:19]

Done.

+};
+
+}  // namespace blink
+
+#endif  // NGBlockChildIterator_h