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

chrome/browser/extensions/extension_webrequest_api_constants.cc

 // Copyright (c) 2010 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.
 
 #include "chrome/browser/extensions/extension_webrequest_api_constants.h"
 
 namespace extension_webrequest_api_constants {
 
 const char kErrorKey[] = "error";
 const char kIpKey[] = "ip";
 const char kMethodKey[] = "method";
 const char kRedirectUrlKey[] = "redirectUrl";
 const char kRequestIdKey[] = "requestId";
 const char kStatusCodeKey[] = "statusCode";
 const char kTabIdKey[] = "tabId";
 const char kTimeStampKey[] = "timeStamp";
 const char kTypeKey[] = "type";
 const char kUrlKey[] = "url";
 
 const char kOnBeforeRedirect[] = "experimental.webRequest.onBeforeRedirect";
 const char kOnBeforeRequest[] = "experimental.webRequest.onBeforeRequest";
+const char kOnBeforeSendHeaders[] =
+    "experimental.webRequest.onBeforeSendHeaders";
 const char kOnCompleted[] = "experimental.webRequest.onCompleted";
 const char kOnErrorOccurred[] = "experimental.webRequest.onErrorOccurred";
 const char kOnHeadersReceived[] = "experimental.webRequest.onHeadersReceived";
 const char kOnRequestSent[] = "experimental.webRequest.onRequestSent";
 
 }  // namespace extension_webrequest_api_constants