fail early if coincidence can't be resolved

src/pathops/SkOpSegment.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #ifndef SkOpSegment_DEFINE
 #define SkOpSegment_DEFINE
 
 #include "SkOpAngle.h"
@@ skipping 266 matching lines @@
     void addCurveTo(int start, int end, SkPathWriter* path, bool active) const;
     void addEndSpan(int endIndex);
     void addLine(const SkPoint pts[2], bool operand, bool evenOdd);
     void addOtherT(int index, double otherT, int otherIndex);
     void addQuad(const SkPoint pts[3], bool operand, bool evenOdd);
     void addSimpleAngle(int endIndex);
     int addSelfT(const SkPoint& pt, double newT);
     void addStartSpan(int endIndex);
     int addT(SkOpSegment* other, const SkPoint& pt, double newT);
     void addTCancel(const SkPoint& startPt, const SkPoint& endPt, SkOpSegment* other);
-    void addTCoincident(const SkPoint& startPt, const SkPoint& endPt, double endT,
+    bool addTCoincident(const SkPoint& startPt, const SkPoint& endPt, double endT,
                         SkOpSegment* other);
     const SkOpSpan* addTPair(double t, SkOpSegment* other, double otherT, bool borrowWind,
                              const SkPoint& pt);
     const SkOpSpan* addTPair(double t, SkOpSegment* other, double otherT, bool borrowWind,
                              const SkPoint& pt, const SkPoint& oPt);
     void alignMultiples(SkTDArray<AlignedSpan>* aligned);
     bool alignSpan(int index, double thisT, const SkPoint& thisPt);
     void alignSpanState(int start, int end);
     bool betweenTs(int lesser, double testT, int greater) const;
     void blindCancel(const SkCoincidence& coincidence, SkOpSegment* other);
@@ skipping 248 matching lines @@
     bool fSmall;  // set if some span is small
     bool fTiny;  // set if some span is tiny
 #if defined(SK_DEBUG) || !FORCE_RELEASE
     int fID;
 #endif
 
     friend class PathOpsSegmentTester;
 };
 
 #endif