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

extensions/browser/test_extension_registry_observer.cc

Index: extensions/browser/test_extension_registry_observer.cc
diff --git a/extensions/browser/test_extension_registry_observer.cc b/extensions/browser/test_extension_registry_observer.cc
index d9a1575d16b1f0ae24d4bfa7cdba07ed3f35efeb..c72af273825396c57634c4b713c16485b0d366a1 100644
--- a/extensions/browser/test_extension_registry_observer.cc
+++ b/extensions/browser/test_extension_registry_observer.cc
@@ -12,7 +12,7 @@ namespace extensions {
 class TestExtensionRegistryObserver::Waiter {
  public:
   explicit Waiter(const std::string& extension_id)
-      : observed_(false), runner_(NULL) {}
+      : observed_(false), runner_(nullptr) {}
 
   void Wait() {
     if (observed_)
@@ -27,7 +27,7 @@ class TestExtensionRegistryObserver::Waiter {
 
     if (runner_.get()) {
       runner_->Quit();
-      runner_ = NULL;
+      runner_ = nullptr;
     }
   }