Add back initialization of |dns_resolution_end_time_| in QuicStreamFactory::Job

|dns_resolution_end_time_| is still used in other histograms
(e.g. Net.QuicServerInfo.DiskCacheWaitForDataReadyTime and
Net.QuicSession.HostResolution.HandshakeConfirmedTime).

The initialization is removed in crrev.com/2256803002. This CL adds it back
to maintain correctness of the remaining histograms which are still using this
field.

R=zhongyi@chromium.org

BUG=629384, 637051

Review-Url: https://codereview.chromium.org/2314403006
Cr-Commit-Position: refs/heads/master@{#417355}

net/quic/chromium/quic_stream_factory.cc

@@ -488,6 +488,7 @@ int QuicStreamFactory::Job::DoResolveHost() {
 }
 
 int QuicStreamFactory::Job::DoResolveHostComplete(int rv) {
+  dns_resolution_end_time_ = base::TimeTicks::Now();
   if (rv != OK)
     return rv;