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

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

Index: third_party/WebKit/Source/core/layout/svg/LayoutSVGTextPath.h
diff --git a/third_party/WebKit/Source/core/layout/svg/LayoutSVGTextPath.h b/third_party/WebKit/Source/core/layout/svg/LayoutSVGTextPath.h
index 1d875856e532555d749daaeb112c6e9aa2ff30dc..1fd09f0713ebe455cbb408ee2e753981c0fce746 100644
--- a/third_party/WebKit/Source/core/layout/svg/LayoutSVGTextPath.h
+++ b/third_party/WebKit/Source/core/layout/svg/LayoutSVGTextPath.h
@@ -25,11 +25,37 @@
 
 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 {

[fs, 2016/02/10 19:34:50]

I guess this could go in platform/, but with this being the single user that
seemed like "premature layering". Let me know what you think.

+    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;