Log the QUIC priority when sending requests.

net/quic/quic_http_utils.cc

Index: net/quic/quic_http_utils.cc
diff --git a/net/quic/quic_http_utils.cc b/net/quic/quic_http_utils.cc
index 173403d82dce5b2873ee75dfdaee2e415de59e28..853b0786c39f27568d4ab6fcad3ec4c2af3152de 100644
--- a/net/quic/quic_http_utils.cc
+++ b/net/quic/quic_http_utils.cc
@@ -20,4 +20,14 @@ NET_EXPORT_PRIVATE RequestPriority ConvertQuicPriorityToRequestPriority(
       IDLE : static_cast<RequestPriority>(HIGHEST - priority);
 }
 
+base::Value* QuicRequestNetLogCallback(
+    const SpdyHeaderBlock* headers,
+    QuicPriority priority,
+    NetLog::LogLevel log_level) {
+  base::DictionaryValue* dict = static_cast<base::DictionaryValue*>(
+      SpdyHeaderBlockNetLogCallback(headers, log_level));
+  dict->SetInteger("quic_priority", static_cast<int>(priority));
+  return dict;
+}
+
 }  // namespace net