Allows deferral of a URLRequest just before talking to the network, at

net/url_request/url_request.cc

Index: net/url_request/url_request.cc
diff --git a/net/url_request/url_request.cc b/net/url_request/url_request.cc
index ce267302ee1bd90116606062f2c7695ff537fd4d..ef53cbe194582607f4f97907679ed65a1b43c8a7 100644
--- a/net/url_request/url_request.cc
+++ b/net/url_request/url_request.cc
@@ -198,6 +198,11 @@ void URLRequest::Delegate::OnSSLCertificateError(URLRequest* request,
   request->Cancel();
 }
 
+void URLRequest::Delegate::OnBeforeNetworkStart(URLRequest* request,
+                                                bool* defer) {
+  *defer = false;

[mmenke, 2014/01/07 15:26:23]

"OnReceivedRedirect" assumes defer is initialized to false.  I think we should
be consistent - and having it auto-initialized seems safer to me.

[jkarlin, 2014/01/07 16:19:32]

Done.

+}
+
 ///////////////////////////////////////////////////////////////////////////////
 // URLRequest
 
@@ -225,7 +230,8 @@ URLRequest::URLRequest(const GURL& url,
                                           base::Unretained(this))),
       has_notified_completion_(false),
       received_response_content_length_(0),
-      creation_time_(base::TimeTicks::Now()) {
+      creation_time_(base::TimeTicks::Now()),
+      notified_before_network_start_(false) {
   SIMPLE_STATS_COUNTER("URLRequestCount");
 
   // Sanity check out environment.
@@ -824,6 +830,22 @@ void URLRequest::NotifyReceivedRedirect(const GURL& location,
   }
 }
 
+void URLRequest::NotifyBeforeNetworkStart(bool* defer) {
+  if (delegate_ && !notified_before_network_start_) {
+    notified_before_network_start_ = true;
+    OnCallToDelegate();
+    delegate_->OnBeforeNetworkStart(this, defer);
+    if (!(*defer))

[mmenke, 2014/01/07 15:26:23]

optional nit:  I think !*defer is more common in net, though it's not exactly
common.  If you think this is clearer, I don't feel particularly strongly about
it.

[jkarlin, 2014/01/07 16:19:32]

Done.

+      OnCallToDelegateComplete();
+  }
+}
+
+void URLRequest::ResumeNetworkStart() {
+  DCHECK(job_);

[mmenke, 2014/01/07 15:26:23]

Maybe DCHECK(notified_network_create_stream_);?

I'd also suggest setting notified_network_create_stream_ to true after the call
into the delegate, to make the DCHECK trigger on re-entrancy.  I don't believe
the ResumeNetworkCreateStream DCHECK will trigger in that case, and I'd like to
have some protection against it, at least in debug builds.

We could try and handle that case, but I don't think there's a reason to.

[jkarlin, 2014/01/07 16:19:32]

Done.

+  OnCallToDelegateComplete();
+  job_->ResumeNetworkStart();
+}
+
 void URLRequest::NotifyResponseStarted() {
   int net_error = OK;
   if (!status_.is_success())