Update SkLightingShader to support rotation

include/core/SkPoint3.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkPoint3_DEFINED
 #define SkPoint3_DEFINED
 
@@ skipping 73 matching lines @@
     }
 
     /** Returns a new point whose coordinates are the sum of a and b (a + b)
     */
     friend SkPoint3 operator+(const SkPoint3& a, const SkPoint3& b) {
         SkPoint3 v;
         v.set(a.fX + b.fX, a.fY + b.fY, a.fZ + b.fZ);
         return v;
     }
 
+    /** Add v's coordinates to the point's
+    */
+    void operator+=(const SkPoint3& v) {
+        fX += v.fX;
+        fY += v.fY;
+        fZ += v.fZ;
+    }
+
+    /** Subtract v's coordinates from the point's
+    */
+    void operator-=(const SkPoint3& v) {
+        fX -= v.fX;
+        fY -= v.fY;
+        fZ -= v.fZ;
+    }
+
     /** Returns the dot product of a and b, treating them as 3D vectors
     */
     static SkScalar DotProduct(const SkPoint3& a, const SkPoint3& b) {
         return a.fX * b.fX + a.fY * b.fY + a.fZ * b.fZ;
     }
 
     SkScalar dot(const SkPoint3& vec) const {
         return DotProduct(*this, vec);
     }
 };
 
 typedef SkPoint3 SkVector3;
 typedef SkPoint3 SkColor3f;
 
 #endif