remove unused code

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 456 matching lines @@
     double a = src[0];
     double b = src[2];
     double c = src[4];
     double d = src[6];
     return 3 * ((b - a) * one_t * one_t + 2 * (c - b) * t * one_t + (d - c) * t * t);
 }
 
 // OPTIMIZE? compute t^2, t(1-t), and (1-t)^2 and pass them to another version of derivative at t?
 SkDVector SkDCubic::dxdyAtT(double t) const {
     SkDVector result = { derivative_at_t(&fPts[0].fX, t), derivative_at_t(&fPts[0].fY, t) };
+    if (result.fX == 0 && result.fY == 0) {
+        if (t == 0) {
+            result = fPts[2] - fPts[0];
+        } else if (t == 1) {
+            result = fPts[3] - fPts[1];
+        } else {
+            // incomplete
+            SkDebugf("!c");
+        }
+        if (result.fX == 0 && result.fY == 0 && zero_or_one(t)) {
+            result = fPts[3] - fPts[0];
+        }
+    }
     return result;
 }
 
 // OPTIMIZE? share code with formulate_F1DotF2
 int SkDCubic::findInflections(double tValues[]) const {
     double Ax = fPts[1].fX - fPts[0].fX;
     double Ay = fPts[1].fY - fPts[0].fY;
     double Bx = fPts[2].fX - 2 * fPts[1].fX + fPts[0].fX;
     double By = fPts[2].fY - 2 * fPts[1].fY + fPts[0].fY;
     double Cx = fPts[3].fX + 3 * (fPts[1].fX - fPts[2].fX) - fPts[0].fX;
@@ skipping 192 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;
 }