fix cubic linear test

src/pathops/SkPathOpsCubic.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #include "SkGeometry.h"
 #include "SkLineParameters.h"
 #include "SkPathOpsConic.h"
 #include "SkPathOpsCubic.h"
@@ skipping 194 matching lines @@
 bool SkDCubic::hullIntersects(const SkDQuad& quad, bool* isLinear) const {
     return hullIntersects(quad.fPts, quad.kPointCount, isLinear);
 }
 
 bool SkDCubic::hullIntersects(const SkDConic& conic, bool* isLinear) const {
 
     return hullIntersects(conic.fPts, isLinear);
 }
 
 bool SkDCubic::isLinear(int startIndex, int endIndex) const {
+    if (fPts[0].approximatelyDEqual(fPts[3]))  {
+        return ((const SkDQuad *) this)->isLinear(0, 2);
+    }
     SkLineParameters lineParameters;
     lineParameters.cubicEndPoints(*this, startIndex, endIndex);
     // FIXME: maybe it's possible to avoid this and compare non-normalized
     lineParameters.normalize();
     double tiniest = SkTMin(SkTMin(SkTMin(SkTMin(SkTMin(SkTMin(SkTMin(fPts[0].fX, fPts[0].fY),
             fPts[1].fX), fPts[1].fY), fPts[2].fX), fPts[2].fY), fPts[3].fX), fPts[3].fY);
     double largest = SkTMax(SkTMax(SkTMax(SkTMax(SkTMax(SkTMax(SkTMax(fPts[0].fX, fPts[0].fY),
             fPts[1].fX), fPts[1].fY), fPts[2].fX), fPts[2].fY), fPts[3].fX), fPts[3].fY);
     largest = SkTMax(largest, -tiniest);
     double distance = lineParameters.controlPtDistance(*this, 1);
@@ skipping 469 matching lines @@
     for (int index = 0; index < roots; ++index) {
         double t = startT + (endT - startT) * extremeTs[index];
         SkDPoint mid = dCurve.ptAtT(t);
         if (topPt->fY > mid.fY || (topPt->fY == mid.fY && topPt->fX > mid.fX)) {
             topT = t;
             *topPt = mid;
         }
     }
     return topT;
 }