Style Change: NULL->nullptr
DOCS_PREVIEW= https://skia.org/?cl=1316233002

Review URL: https://codereview.chromium.org/1316233002
diff --git a/gm/addarc.cpp b/gm/addarc.cpp
index 3bfed8d..0d1ea93 100644
--- a/gm/addarc.cpp
+++ b/gm/addarc.cpp
@@ -101,7 +101,7 @@
             SkPathMeasure meas(path, false);
             SkScalar arcLen = rad * R;
             SkPoint pos;
-            if (meas.getPosTan(arcLen, &pos, NULL)) {
+            if (meas.getPosTan(arcLen, &pos, nullptr)) {
                 canvas->drawLine(0, 0, pos.x(), pos.y(), measPaint);
             }
         }