Fix recursion bug in blocking a fetch and add a test

headless/public/util/url_fetcher.h

Index: headless/public/util/url_fetcher.h
diff --git a/headless/public/util/url_fetcher.h b/headless/public/util/url_fetcher.h
index abb8dfed13d5c136b17b8e93e4bbe09f2030562d..115302f6d607f5a229d142df25e47ef0f9fe61b7 100644
--- a/headless/public/util/url_fetcher.h
+++ b/headless/public/util/url_fetcher.h
@@ -35,7 +35,7 @@ class URLFetcher {
     ResultListener() {}
 
     // Informs the listener that the fetch failed.
-    virtual void OnStartError(net::Error error) = 0;
+    virtual void OnFetchStartError(net::Error error) = 0;
 
     // Informs the listener that the fetch succeeded and returns the HTTP
     // headers and the body.  NOTE |body| must be owned by the caller and remain