[LayoutNG] A different approach to multi-col.

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

Index: third_party/WebKit/Source/core/layout/ng/ng_block_layout_child_iterator.h
diff --git a/third_party/WebKit/Source/core/layout/ng/ng_block_layout_child_iterator.h b/third_party/WebKit/Source/core/layout/ng/ng_block_layout_child_iterator.h
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index 0000000000000000000000000000000000000000..3af4a5320800fb59129e44d92d80d34fd7844ef9
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+++ b/third_party/WebKit/Source/core/layout/ng/ng_block_layout_child_iterator.h
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+// 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 NGBlockLayoutChildIterator_h
+#define NGBlockLayoutChildIterator_h
+
+#include "core/layout/ng/ng_block_break_token.h"
+#include "core/layout/ng/ng_layout_input_node.h"
+
+namespace blink {
+
+class NGBlockLayoutChildIterator {
+ public:
+  NGBlockLayoutChildIterator(NGLayoutInputNode* first_child,
+                             NGBlockBreakToken* break_token)
+      : child_(first_child), break_token_(break_token), child_token_idx_(0) {
+    Advance();
+  }
+
+  std::pair<NGLayoutInputNode*, NGBreakToken*> NextChild() {
+    NGLayoutInputNode* child = child_;
+    NGBreakToken* child_token = child_token_;
+    if (child_)
+      child_ = child_->NextSibling();
+    Advance();
+    return std::make_pair(child, child_token);
+  }
+
+ private:
+  //
+  void Advance() {
+    const auto& child_break_tokens = break_token_->ChildBreakTokens();
+    child_token_ = nullptr;
+
+    do {
+      NGBreakToken* next_child_token = nullptr;
+      if (break_token_ && child_token_idx_ < child_break_tokens.size()) {
+        next_child_token = break_token_->ChildBreakTokens()[child_token_idx_];
+      }
+
+      if (next_child_token && next_child_token->Node() == child_) {
+        // If we're resuming layout after a fragmentainer break, we need to skip
+        // siblings that we're done with. We may have been able to fully lay out
+        // some
+        // node(s) preceding a node that we had to break inside (and therefore
+        // were
+        // not able to fully lay out). This happens when we have parallel flows
+        // [1],
+        // which are caused by floats, overflow, etc.
+        //
+        // [1] https://drafts.csswg.org/css-break/#parallel-flows
+
+        // We may have a break token which just represents that a child has
+        // fully completed its layout.
+        if (next_child_token->IsFinished())
+          continue;
+
+        // We've found our next child, return.
+        child_token_idx_++;
+        child_token_ = next_child_token;
+        return;
+      } else {
+        // There is no break token which matches here, we've found our next
+        // child.
+        return;
+      }
+    } while ((child_ = child_->NextSibling()));
+  }
+
+  Persistent<NGLayoutInputNode> child_;
+  Persistent<NGBreakToken> child_token_;
+
+  Persistent<NGBlockBreakToken> break_token_;
+  size_t child_token_idx_;
+};
+
+}  // namespace blink
+
+#endif  // NGBlockLayoutChildIterator_h