[Extension ServiceWorkers] Allow service worker registration

extensions/browser/extension_protocols.cc

Index: extensions/browser/extension_protocols.cc
diff --git a/extensions/browser/extension_protocols.cc b/extensions/browser/extension_protocols.cc
index 8ad21c1d4e0f45668b83ff50eb63ef0912b94fb7..4e8f9d9e3907ca80a251e2906c6ff0a6028448e9 100644
--- a/extensions/browser/extension_protocols.cc
+++ b/extensions/browser/extension_protocols.cc
@@ -195,6 +195,10 @@ class URLRequestExtensionJob : public net::URLRequestFileJob {
     *info = response_info_;
   }
 
+  // This always returns 200 because a URLRequestExtensionJob will only get
+  // created in MaybeCreateJob() if the file exists.
+  int GetResponseCode() const override { return 200; }
+
   void Start() override {
     request_timer_.reset(new base::ElapsedTimer());
     base::FilePath* read_file_path = new base::FilePath;