Added callback to DownloadUrl() so we can find download failures.

net/url_request/url_request.h

Index: net/url_request/url_request.h
diff --git a/net/url_request/url_request.h b/net/url_request/url_request.h
index 2c54cbca5a5ba525c2e2245490d2c5e855af1708..b224fc6f54e5de8a04a1b9d9fc7776c023ece1cf 100644
--- a/net/url_request/url_request.h
+++ b/net/url_request/url_request.h
@@ -324,7 +324,9 @@ class NET_EXPORT URLRequest : NON_EXPORTED_BASE(public base::NonThreadSafe),
   // The chain of urls traversed by this request.  If the request had no
   // redirects, this vector will contain one element.
   const std::vector<GURL>& url_chain() const { return url_chain_; }
-  const GURL& url() const { return url_chain_.back(); }
+  const GURL& url() const {

[cbentzel, 2012/03/08 17:58:48]

Why was this change needed?

[ahendrickson, 2012/03/08 21:33:07]

I was getting a crash because url_chain_ was empty in some test.

[Randy Smith (Not in Mondays), 2012/03/09 19:14:02]

Did you look at why it was empty in those tests when it wasn't before?  I
dislike making production code changes for tests, and I wouldn't have thought
that this CL would result in a change in url_chain_ contents.  And we don't
really have a url_request.h expert on the review list (excepting possibly Chris
:-}).  "If you don't understand it, it's dangerous."

[ahendrickson, 2012/03/09 20:50:08]

No, I didn't.

I've reverted this, and will see if I can reproduce it.

+    return url_chain_.size() ? url_chain_.back() : GURL::EmptyGURL();
+  }
 
   // The URL that should be consulted for the third-party cookie blocking
   // policy.