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

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 7b792a5d5dd2ad98db165fa8262fdef63c582ec9..dc2832fdab150c0cb3e412b1db151ef73be389ce 100644
--- a/net/url_request/url_request.cc
+++ b/net/url_request/url_request.cc
@@ -43,7 +43,8 @@ void StripPostSpecificHeaders(net::HttpRequestHeaders* headers) {
 }
 
 // This counter keeps track of the identifiers used for URL requests so far.
-uint64 g_next_url_request_identifier = 0;
+// 0 is reserved to represent an invalid ID.
+uint64 g_next_url_request_identifier = 1;
 
 // This lock protects g_next_url_request_identifier.
 base::Lock g_next_url_request_identifier_lock;