Fix quad convexity with only one backward dir

src/core/SkPath.cpp

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include <cmath>
 #include "SkBuffer.h"
 #include "SkCubicClipper.h"
@@ skipping 2387 matching lines @@
                 } else if (dir != fExpectedDir) {
                     fConvexity = SkPath::kConcave_Convexity;
                     fFirstDirection = SkPathPriv::kUnknown_FirstDirection;
                 }
                 fLastVec = vec;
                 break;
             case kStraight_DirChange:
                 break;
             case kBackwards_DirChange:
                 if (fIsCurve) {
-                    fConvexity = SkPath::kConcave_Convexity;
-                    fFirstDirection = SkPathPriv::kUnknown_FirstDirection;
+                    // If any of the subsequent dir is non-backward, it'll be concave.
+                    // Otherwise, it's still convex.
+                    fExpectedDir = dir;
                 }
                 fLastVec = vec;
                 break;
             case kInvalid_DirChange:
                 SkFAIL("Use of invalid direction change flag");
                 break;
         }
     }
 
     SkPoint             fPriorPt;
@@ skipping 970 matching lines @@
         path->arcTo(oval, startAngle, 180.f, false);
         startAngle += 180.f;
         forceMoveTo = false;
         sweepAngle -= 360.f;
     }
     path->arcTo(oval, startAngle, sweepAngle, forceMoveTo);
     if (useCenter) {
         path->close();
     }
 }