Replace s/NULL/nullptr/ in field initializers used in constructors.

This change has been generated by a clang tool developed for the
go/miracleptr project.

Bug: 1080832
Change-Id: Ie7f428c8ad300db1df95d873668163d0ac719a22
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2231843
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Bartek Nowierski <bartekn@chromium.org>
Commit-Queue: Ɓukasz Anforowicz <lukasza@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#776343}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: c695e53d889f36d33293a14f2a57ef1ab75d7a40
diff --git a/xdisplaycheck.cc b/xdisplaycheck.cc
index 6623153..2e901ee 100644
--- a/xdisplaycheck.cc
+++ b/xdisplaycheck.cc
@@ -36,7 +36,7 @@
 
 class XScopedDisplay {
  public:
-  XScopedDisplay() : display_(NULL) {}
+  XScopedDisplay() : display_(nullptr) {}
   ~XScopedDisplay() {
     if (display_) XCloseDisplay(display_);
   }