Update SkLightingShader to support rotation

src/core/SkPoint3.h

Index: src/core/SkPoint3.h
diff --git a/include/effects/SkPoint3.h b/src/core/SkPoint3.h
similarity index 90%
rename from include/effects/SkPoint3.h
rename to src/core/SkPoint3.h
index f31f8207ab94aa8d02453cc36f8b09a57e467510..af24a8df58eac82c5987d7540f43e089df2bf87e 100644
--- a/include/effects/SkPoint3.h
+++ b/src/core/SkPoint3.h
@@ -91,6 +91,22 @@ struct SK_API SkPoint3 {
         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) {