Move seg_to to a new header, define SkSegType enum there

src/core/SkPathMeasurePriv.h

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkPathMeasurePriv_DEFINED
+#define SkPathMeasurePriv_DEFINED
+
+#include "SkPath.h"
+#include "SkPoint.h"
+#include "SkGeometry.h"
+
+// Used in the Segment struct defined in SkPathMeasure.h
+// It is used as a 2-bit field so if you add to this
+// you must increase the size of the bitfield there.
+enum SkSegType {
+    kLine_SegType,
+    kQuad_SegType,
+    kCubic_SegType,
+    kConic_SegType,
+};
+
+
+void SkPathMeasure_segTo(const SkPoint pts[], unsigned segType,
+                   SkScalar startT, SkScalar stopT, SkPath* dst);
+
+#endif  // SkPathMeasurePriv_DEFINED