Removing AccessLog class. This is a partial revert of yzshen's r74872.

net/url_request/url_request_throttler_manager.h

Index: net/url_request/url_request_throttler_manager.h
diff --git a/net/url_request/url_request_throttler_manager.h b/net/url_request/url_request_throttler_manager.h
index 456e84cdc276753af4df228854349e4ce0175b57..58d1985908af9f6a7da0690f4e1037bcb0a51347 100644
--- a/net/url_request/url_request_throttler_manager.h
+++ b/net/url_request/url_request_throttler_manager.h
@@ -102,12 +102,6 @@ class URLRequestThrottlerManager {
   // period.
   bool enforce_throttling_;
 
-  // Whether to record threads that have accessed the URLRequestThrottlerManager
-  // singleton object.
-  // TODO(yzshen): It is used for diagnostic purpose and should be removed once
-  // we figure out crbug.com/71721
-  bool record_access_log_;
-
   DISALLOW_COPY_AND_ASSIGN(URLRequestThrottlerManager);
 };