Implement exponential back-off mechanism.

net/url_request/url_request_http_job.h

Index: net/url_request/url_request_http_job.h
diff --git a/net/url_request/url_request_http_job.h b/net/url_request/url_request_http_job.h
index 431756ad103f927ece3c5c3fe7f9973eb803db26..c981047150177af37a88804096e88df0fa81cfb9 100644
--- a/net/url_request/url_request_http_job.h
+++ b/net/url_request/url_request_http_job.h
@@ -15,6 +15,7 @@
 #include "net/base/completion_callback.h"
 #include "net/http/http_request_info.h"
 #include "net/url_request/url_request_job.h"
+#include "net/url_request/url_request_throttler_entry_interface.h"
 
 namespace net {
 class HttpResponseInfo;
@@ -112,6 +113,9 @@ class URLRequestHttpJob : public URLRequestJob {
 
   scoped_ptr<net::HttpTransaction> transaction_;
 
+  // This is used to supervise traffic and enforce exponential back-off.
+  scoped_refptr<net::URLRequestThrottlerEntryInterface> 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