Allow CertNetFetcher to be shutdown from the network thread

net/test/url_request/url_request_hanging_read_job.cc

Index: net/test/url_request/url_request_hanging_read_job.cc
diff --git a/net/test/url_request/url_request_hanging_read_job.cc b/net/test/url_request/url_request_hanging_read_job.cc
index 74c680f241877afa2be459aa9ea154a958c77742..5223b297b4502e95ebdbc4c1bf132cf837b8b75a 100644
--- a/net/test/url_request/url_request_hanging_read_job.cc
+++ b/net/test/url_request/url_request_hanging_read_job.cc
@@ -92,6 +92,8 @@ void URLRequestHangingReadJob::GetResponseInfoConst(
 }
 
 void URLRequestHangingReadJob::StartAsync() {
+  if (is_done())

[estark, 2016/12/21 20:02:59]

This is a little weird. I added it because
CertNetFetcherImplTest.ShutdownCancelsRequests has the following sequence of
events:
- DoFetch queues a DoFetchOnNetworkThread task
- The test queues a Shutdown task on the network thread
- DoFetchOnNetworkThread task runs, queuing a StartAsync task
- Shutdown task runs, cancelling the URLRequest
- StartAsync task runs. NotifyHeadersComplete() is not supposed to be called if
the request has been cancelled, which is why I needed to add this is_done()
check.

+    return;
   set_expected_content_size(content_length_);
   NotifyHeadersComplete();
 }