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

extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.cc

Index: extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.cc
diff --git a/extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.cc b/extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.cc
index 9e094127a7a6b1a0f3017dd1bdc6a2426422b2ff..04740cfc85e0734cf28c65ade5659a59be459119 100644
--- a/extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.cc
+++ b/extensions/browser/guest_view/mime_handler_view/mime_handler_view_guest.cc
@@ -31,7 +31,7 @@ GuestViewBase* MimeHandlerViewGuest::Create(
     content::BrowserContext* browser_context,
     int guest_instance_id) {
   if (!extensions::FeatureSwitch::mime_handler_view()->IsEnabled())
-    return NULL;
+    return nullptr;
 
   return new MimeHandlerViewGuest(browser_context, guest_instance_id);
 }
@@ -71,7 +71,7 @@ void MimeHandlerViewGuest::CreateWebContents(
 
   GURL mime_handler_extension_url(extension_src);
   if (!mime_handler_extension_url.is_valid()) {
-    callback.Run(NULL);
+    callback.Run(nullptr);
     return;
   }
 
@@ -83,7 +83,7 @@ void MimeHandlerViewGuest::CreateWebContents(
   if (!mime_handler_extension) {
     LOG(ERROR) << "Extension for mime_type not found, mime_type = "
                << orig_mime_type;
-    callback.Run(NULL);
+    callback.Run(nullptr);
     return;
   }