[LayoutNG] Allow block-flow layout to be fragmented using new approach.

third_party/WebKit/Source/core/layout/ng/ng_column_mapper.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 NGColumnMapper_h
-#define NGColumnMapper_h
-
-#include "core/CoreExport.h"
-#include "core/layout/ng/ng_block_break_token.h"
-#include "platform/heap/Handle.h"
-
-namespace blink {
-
-// Keeps track of the current column, and is used to map offsets from the
-// coordinate established by the fragmented flow [1] to visual coordinates.
-//
-// [1] https://drafts.csswg.org/css-break/#fragmented-flow
-//
-// TODO(mstensho): Add a NGFragmentainerMapper super class. There are other
-// fragmentation types than multicol (regions, pagination for printing).
-class CORE_EXPORT NGColumnMapper
-    : public GarbageCollectedFinalized<NGColumnMapper> {
- public:
-  NGColumnMapper(LayoutUnit inline_progression, LayoutUnit block_size)
-      : inline_progression_(inline_progression), block_size_(block_size) {}
-
-  // Column block length.
-  LayoutUnit BlockSize() const { return block_size_; }
-
-  // Offset for next break, in the fragmented flow coordinate space.
-  LayoutUnit NextBreakOffset() const {
-    return last_break_block_offset_ + block_size_;
-  }
-
-  // Convert an offset in the fragmented flow coordinate space to the visual
-  // coordinate space.
-  void ToVisualOffset(NGLogicalOffset& offset) {
-    offset.inline_offset += inline_offset_;
-    offset.block_offset -= last_break_block_offset_;
-  }
-
-  // Specify where in the content to start layout of the next column.
-  void SetBreakToken(NGBlockBreakToken* token) {
-    DCHECK(!break_token_);
-    break_token_ = token;
-  }
-  bool HasBreakToken() const { return break_token_; }
-
-  // Advance to the next column. Returns the break token to resume at. If
-  // nullptr is returned, there's no more content to process.
-  NGBlockBreakToken* Advance() {
-    NGBlockBreakToken* token = break_token_;
-    break_token_ = nullptr;
-    if (token) {
-      inline_offset_ += inline_progression_;
-      last_break_block_offset_ += block_size_;
-    }
-    return token;
-  }
-
-  DEFINE_INLINE_TRACE() { visitor->trace(break_token_); }
-
- private:
-  // Where to resume in the next column.
-  Member<NGBlockBreakToken> break_token_;
-
-  // The sum of used column-width and column_gap.
-  LayoutUnit inline_progression_;
-
-  // Inline offset to the current column.
-  LayoutUnit inline_offset_;
-
-  // Block size of a column.
-  LayoutUnit block_size_;
-
-  // Amount of content held by previous columns.
-  LayoutUnit last_break_block_offset_;
-};
-
-}  // namespace blink
-
-#endif  // NGColumnMapper_h