First pass at adding http/backend cache to NetLog

net/base/net_log.h

Index: net/base/net_log.h
===================================================================
--- net/base/net_log.h	(revision 68857)
+++ net/base/net_log.h	(working copy)
@@ -193,6 +193,12 @@
   void EndEvent(NetLog::EventType event_type,
                 const scoped_refptr<NetLog::EventParameters>& params) const;
 
+  // Just like EndEvent, except |net_error| is a net error code.  If it's
+  // negative, a parameter called "net_error" with a value of |net_error| is
+  // associated with the event.  Otherwise, the end event has no parameters.
+  // |net_error| must not be ERR_IO_PENDING, as it's not a true error.
+  void EndEventWithErrorCode(NetLog::EventType event_type, int net_error) const;
+
   NetLog::LogLevel GetLogLevel() const;
 
   // Returns true if the log level is LOG_ALL.