Introduce a delegate to avoid hardcoding "chrome-extension" in net/.

net/url_request/url_request_throttler_manager.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_URL_REQUEST_URL_REQUEST_THROTTLER_MANAGER_H_
 #define NET_URL_REQUEST_URL_REQUEST_THROTTLER_MANAGER_H_
 #pragma once
 
 #include <map>
 #include <set>
 #include <string>
 
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
 #include "base/threading/non_thread_safe.h"
 #include "base/threading/platform_thread.h"
 #include "googleurl/src/gurl.h"
 #include "net/base/net_export.h"
 #include "net/base/network_change_notifier.h"
 #include "net/url_request/url_request_throttler_entry.h"
 
 namespace net {
 
 class BoundNetLog;
 class NetLog;
 
+class NET_EXPORT URLRequestThrottlerManagerDelegate {
+ public:
+  virtual ~URLRequestThrottlerManagerDelegate() {}
+
+  // Returns true if the URLRequestThrottlerManager may reject the
+  // request in question if it believe the server servicing the
+  // request to be overloaded or down.
+  virtual bool MayRejectRequest(URLRequest* request) = 0;

[eroman, 2012/06/05 05:30:25]

Same comment as earlier, please make |request| const. If delegates can cancel or
change the request, that complicates things. And I don't think it is necessary
here.

[Jói, 2012/06/05 16:39:14]

Done.

+};
+
 // Class that registers URL request throttler entries for URLs being accessed
 // in order to supervise traffic. URL requests for HTTP contents should
 // register their URLs in this manager on each request.
 //
 // URLRequestThrottlerManager maintains a map of URL IDs to URL request
 // throttler entries. It creates URL request throttler entries when new URLs
 // are registered, and does garbage collection from time to time in order to
 // clean out outdated entries. URL ID consists of lowercased scheme, host, port
 // and path. All URLs converted to the same ID will share the same entry.
 class NET_EXPORT URLRequestThrottlerManager
     : NON_EXPORTED_BASE(public base::NonThreadSafe),
       public NetworkChangeNotifier::IPAddressObserver,
       public NetworkChangeNotifier::ConnectionTypeObserver {
  public:
-  URLRequestThrottlerManager();
+  explicit URLRequestThrottlerManager(
+      URLRequestThrottlerManagerDelegate* delegate);

[eroman, 2012/06/05 05:30:25]

Please describe ownership semantics (i.e. that |delegate| must remain alive). I
know this is following standard model, but always helps to document it anyway
for readers.

[Jói, 2012/06/05 16:39:14]

This concern goes away with the switch to NetworkDelegate, since I now retrieve
that when needed via the URLRequest's URLRequestContext.

   virtual ~URLRequestThrottlerManager();
 
   // Must be called for every request, returns the URL request throttler entry
   // associated with the URL. The caller must inform this entry of some events.
   // Please refer to url_request_throttler_entry_interface.h for further
   // informations.
   scoped_refptr<URLRequestThrottlerEntryInterface> RegisterRequestUrl(
       const GURL& url);
 
   // Adds the given host to a list of sites for which exponential back-off
@@ skipping 54 matching lines @@
   // we were previously getting 500 or 503 responses from (perhaps the
   // responses are from a badly-written proxy that should have returned a
   // 502 or 504 because it's upstream connection was down or it had no route
   // to the server).
   void OnNetworkChange();
 
   // Used by tests.
   int GetNumberOfEntriesForTests() const { return url_entries_.size(); }
 
  private:
+  friend class URLRequestThrottlerEntry;
+
   // From each URL we generate an ID composed of the scheme, host, port and path
   // that allows us to uniquely map an entry to it.
   typedef std::map<std::string, scoped_refptr<URLRequestThrottlerEntry> >
       UrlEntryMap;
 
   // We maintain a set of hosts that have opted out of exponential
   // back-off throttling.
   typedef std::set<std::string> OptOutHosts;
 
   // Maximum number of entries that we are willing to collect in our map.
   static const unsigned int kMaximumNumberOfEntries;
   // Number of requests that will be made between garbage collection.
   static const unsigned int kRequestsBetweenCollecting;
 
   // Map that contains a list of URL ID and their matching
   // URLRequestThrottlerEntry.
   UrlEntryMap url_entries_;
 
   // Set of hosts that have opted out.
   OptOutHosts opt_out_hosts_;
 
   // This keeps track of how many requests have been made. Used with
   // GarbageCollectEntries.
   unsigned int requests_since_last_gc_;
 
   // Valid after construction.
   GURL::Replacements url_id_replacements_;
 
-  // Whether we would like to reject outgoing HTTP requests during the back-off
-  // period.
-  bool enforce_throttling_;
-
   // Certain tests do not obey the net component's threading policy, so we
   // keep track of whether we're being used by tests, and turn off certain
   // checks.
   //
   // TODO(joi): See if we can fix the offending unit tests and remove this
   // workaround.
   bool enable_thread_checks_;
 
   // Initially false, switches to true once we have logged because of back-off
   // being disabled for localhost.
   bool logged_for_localhost_disabled_;
 
   // NetLog to use, if configured.
   BoundNetLog net_log_;
 
   // Valid once we've registered for network notifications.
   base::PlatformThreadId registered_from_thread_;
 
+  URLRequestThrottlerManagerDelegate* delegate_;
+
   DISALLOW_COPY_AND_ASSIGN(URLRequestThrottlerManager);
 };
 
 }  // namespace net
 
 #endif  // NET_URL_REQUEST_URL_REQUEST_THROTTLER_MANAGER_H_