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

extensions/common/manifest_handlers/icons_handler.cc

Index: extensions/common/manifest_handlers/icons_handler.cc
diff --git a/extensions/common/manifest_handlers/icons_handler.cc b/extensions/common/manifest_handlers/icons_handler.cc
index c8e01d4cb5198c160a754cc190f980058c87baca..f8f0566061d554c370f7e5328cfae7962100b36d 100644
--- a/extensions/common/manifest_handlers/icons_handler.cc
+++ b/extensions/common/manifest_handlers/icons_handler.cc
@@ -57,7 +57,7 @@ IconsHandler::~IconsHandler() {
 
 bool IconsHandler::Parse(Extension* extension, base::string16* error) {
   scoped_ptr<IconsInfo> icons_info(new IconsInfo);
-  const base::DictionaryValue* icons_dict = NULL;
+  const base::DictionaryValue* icons_dict = nullptr;
   if (!extension->manifest()->GetDictionary(keys::kIcons, &icons_dict)) {
     *error = base::ASCIIToUTF16(manifest_errors::kInvalidIcons);
     return false;