Implement exponential back-off mechanism and enforce it at the URLRequestHttpJob level.

net/url_request/url_request_http_job.h

Index: net/url_request/url_request_http_job.h
===================================================================
--- net/url_request/url_request_http_job.h	(revision 64189)
+++ net/url_request/url_request_http_job.h	(working copy)
@@ -14,6 +14,7 @@
 #include "net/base/auth.h"
 #include "net/base/completion_callback.h"
 #include "net/http/http_request_info.h"
+#include "net/request_throttler/request_throttler_entry_interface.h"
 #include "net/url_request/url_request_job.h"
 
 namespace net {
@@ -112,6 +113,9 @@
 
   scoped_ptr<net::HttpTransaction> transaction_;
 
+  // This is used to supervise traffic and enforce exponential back-off.
+  scoped_refptr<RequestThrottlerEntryInterface> throttling_entry_;
+
   // Indicated if an SDCH dictionary was advertised, and hence an SDCH
   // compressed response is expected.  We use this to help detect (accidental?)
   // proxy corruption of a response, which sometimes marks SDCH content as