Add a link to design doc for NetLog.

net/base/net_log.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_BASE_NET_LOG_H_
 #define NET_BASE_NET_LOG_H_
 #pragma once
 
 #include <string>
 
@@ skipping 15 matching lines @@
 // NetLog is the destination for log messages generated by the network stack.
 // Each log message has a "source" field which identifies the specific entity
 // that generated the message (for example, which URLRequest or which
 // SocketStream).
 //
 // To avoid needing to pass in the "source ID" to the logging functions, NetLog
 // is usually accessed through a BoundNetLog, which will always pass in a
 // specific source ID.
 //
 // All NetLog methods must be thread-safe.
+//
+// For a broader introduction see the design document:
+// https://sites.google.com/a/chromium.org/dev/developers/design-documents/network-stack/netlog
 class NET_EXPORT NetLog {
  public:
   enum EventType {
 #define EVENT_TYPE(label) TYPE_ ## label,
 #include "net/base/net_log_event_type_list.h"
 #undef EVENT_TYPE
     EVENT_COUNT
   };
 
   // The 'phase' of an event trace (whether it marks the beginning or end
@@ skipping 426 matching lines @@
   virtual ~NetLogSourceParameter() {}
 
  private:
   const char* name_;
   const NetLog::Source value_;
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_NET_LOG_H_