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

chrome/browser/extensions/extension_webrequest_api_constants.cc

Index: chrome/browser/extensions/extension_webrequest_api_constants.cc
diff --git a/chrome/browser/extensions/extension_webrequest_api_constants.cc b/chrome/browser/extensions/extension_webrequest_api_constants.cc
index 38ad85d321d32fccd9ca2143d6a5c6fb6354a419..6a2b93268090f54973d8ca841eb2f61d595fbad3 100644
--- a/chrome/browser/extensions/extension_webrequest_api_constants.cc
+++ b/chrome/browser/extensions/extension_webrequest_api_constants.cc
@@ -19,6 +19,8 @@ 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";