Factor out the <textPath> positioning mapping code into a helper class

third_party/WebKit/Source/core/layout/svg/LayoutSVGTextPath.h

 /*
  * Copyright (C) 2007 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2009 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  */
 
 #ifndef LayoutSVGTextPath_h
 #define LayoutSVGTextPath_h
 
 #include "core/layout/svg/LayoutSVGInline.h"
 
 namespace blink {
 
+// This class maps a 1D location in the "path space"; [0, path length] to a
+// (2D) point on the path and provides the normal (angle from the x-axis) for
+// said point.
+class PathPositionMapper {
+    USING_FAST_MALLOC(PathPositionMapper);
+public:
+    static PassOwnPtr<PathPositionMapper> create(const Path& path)
+    {
+        return adoptPtr(new PathPositionMapper(path));
+    }
+
+    enum PositionType {
+        OnPath,
+        BeforePath,
+        AfterPath,
+    };
+    PositionType pointAndNormalAtLength(float length, FloatPoint&, float& angle);
+    float length() const { return m_pathLength; }
+
+private:
+    explicit PathPositionMapper(const Path&);
+
+    Path::PositionCalculator m_positionCalculator;
+    float m_pathLength;
+};
+
 class LayoutSVGTextPath final : public LayoutSVGInline {
 public:
     explicit LayoutSVGTextPath(Element*);
 
-    Path layoutPath() const;
+    PassOwnPtr<PathPositionMapper> layoutPath() const;
     float calculateStartOffset(float) const;
 
     bool isChildAllowed(LayoutObject*, const ComputedStyle&) const override;
 
     bool isOfType(LayoutObjectType type) const override { return type == LayoutObjectSVGTextPath || LayoutSVGInline::isOfType(type); }
 
     const char* name() const override { return "LayoutSVGTextPath"; }
 };
 
 DEFINE_LAYOUT_OBJECT_TYPE_CASTS(LayoutSVGTextPath, isSVGTextPath());
 
 } // namespace blink
 
 #endif // LayoutSVGTextPath_h