Run clang-modernize -use-nullptr over src/extensions/.

extensions/test/result_catcher.cc

Index: extensions/test/result_catcher.cc
diff --git a/extensions/test/result_catcher.cc b/extensions/test/result_catcher.cc
index 5dc84a824ae6d9710133c052142f90fe2d06a7d4..e55076b99a95fb4bfb3a5a3a1f132446afd14b89 100644
--- a/extensions/test/result_catcher.cc
+++ b/extensions/test/result_catcher.cc
@@ -11,7 +11,7 @@
 namespace extensions {
 
 ResultCatcher::ResultCatcher()
-    : browser_context_restriction_(NULL), waiting_(false) {
+    : browser_context_restriction_(nullptr), waiting_(false) {
   registrar_.Add(this,
                  extensions::NOTIFICATION_EXTENSION_TEST_PASSED,
                  content::NotificationService::AllSources());