Add the UMA recording recall of URLRequests preconnected.

net/base/network_delegate.cc

Index: net/base/network_delegate.cc
diff --git a/net/base/network_delegate.cc b/net/base/network_delegate.cc
index 5a69b863e62ef8394d9e646fbc102aea7d8f47bc..0fafcbc89a6255dd41b121bbe0ed6c0d43de39ea 100644
--- a/net/base/network_delegate.cc
+++ b/net/base/network_delegate.cc
@@ -10,6 +10,11 @@
 
 namespace net {
 
+void NetworkDelegate::NotifyBeforePreconnect(const GURL& url) {
+  DCHECK(CalledOnValidThread());
+  OnBeforePreconnect(url);
+}
+
 int NetworkDelegate::NotifyBeforeURLRequest(
     URLRequest* request, const CompletionCallback& callback,
     GURL* new_url) {