Fix a crash in URLFetcherCore by handling a case where |request_| is NULL

net/url_request/url_fetcher_core.cc

Index: net/url_request/url_fetcher_core.cc
diff --git a/net/url_request/url_fetcher_core.cc b/net/url_request/url_fetcher_core.cc
index bd28b4b0161af2c205a3c2cd1766fbc15ef5ab3d..1cfda7487cf7dc8f23ac32e37610b483c957078d 100644
--- a/net/url_request/url_fetcher_core.cc
+++ b/net/url_request/url_fetcher_core.cc
@@ -832,6 +832,8 @@ void URLFetcherCore::DidWriteBuffer(scoped_refptr<DrainableIOBuffer> data,
 }
 
 void URLFetcherCore::ReadResponse() {
+  if (!request_.get())
+    return;

[mmenke, 2013/10/31 18:14:18]

I'd really like to just delete the writer on cancellation - the writer does
nominally support deletion while a request is pending, but I believe there's
another bug in that case - It would work if it had a SequencedTaskRunner.  We
also currently never reset the writer, which makes me a little nervous about
that option.

So...  I think it's OK to check the request instead, but if we go that route,
I'd rather it be in URLFetcherCore::DidWriteBuffer.

[droger, 2013/11/04 15:38:04]

Done.

   // Some servers may treat HEAD requests as GET requests.  To free up the
   // network connection as soon as possible, signal that the request has
   // completed immediately, without trying to read any data back (all we care