Add request_id to HttpRequestInfo and pass it to the NetworkDelegate for events.

net/http/http_request_info.h

Index: net/http/http_request_info.h
diff --git a/net/http/http_request_info.h b/net/http/http_request_info.h
index 70c13008daa1c215217ee69456a81942d5156f1e..b906cf5407fc1fa0b6cce98625f26cb562187c7b 100644
--- a/net/http/http_request_info.h
+++ b/net/http/http_request_info.h
@@ -52,6 +52,10 @@ struct HttpRequestInfo {
 
   // The motivation behind this request.
   RequestMotivation motivation;
+
+  // An optional globally unique identifier for this request for use by the
+  // consumer. 0 is invalid.
+  uint64 request_id;
 };
 
 }  // namespace net