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

extensions/renderer/extension_helper.cc

Index: extensions/renderer/extension_helper.cc
diff --git a/extensions/renderer/extension_helper.cc b/extensions/renderer/extension_helper.cc
index e9da0f58ea5c8ee461d90fb034212e87a2c72220..94a7532694b4b5e5302198b91fa029093cefd1b0 100644
--- a/extensions/renderer/extension_helper.cc
+++ b/extensions/renderer/extension_helper.cc
@@ -110,7 +110,7 @@ content::RenderView* ExtensionHelper::GetBackgroundPage(
   content::RenderView::ForEach(&accumulator);
   CHECK_LE(accumulator.views().size(), 1u);
   if (accumulator.views().size() == 0)
-    return NULL;
+    return nullptr;
   return accumulator.views()[0];
 }