Implement URLRequestBackoffManager for managing Backoff headers

net/url_request/url_request_context_builder.cc

Index: net/url_request/url_request_context_builder.cc
diff --git a/net/url_request/url_request_context_builder.cc b/net/url_request/url_request_context_builder.cc
index 771bc3f25f28e91c929b3e60c4baae85ce8ca54b..ab618ae80e0945081727e2aeb81c6e0b62d07907 100644
--- a/net/url_request/url_request_context_builder.cc
+++ b/net/url_request/url_request_context_builder.cc
@@ -33,6 +33,7 @@
 #include "net/ssl/ssl_config_service_defaults.h"
 #include "net/url_request/data_protocol_handler.h"
 #include "net/url_request/static_http_user_agent_settings.h"
+#include "net/url_request/url_request_backoff_manager.h"
 #include "net/url_request/url_request_context.h"
 #include "net/url_request/url_request_context_storage.h"
 #include "net/url_request/url_request_intercepting_job_factory.h"
@@ -333,6 +334,9 @@ URLRequestContext* URLRequestContextBuilder::Build() {
   if (throttling_enabled_)
     storage->set_throttler_manager(new URLRequestThrottlerManager());
 
+  if (backoff_enabled_)
+    storage->set_backoff_manager(new URLRequestBackoffManager());
+
   HttpNetworkSession::Params network_session_params;
   network_session_params.host_resolver = context->host_resolver();
   network_session_params.cert_verifier = context->cert_verifier();