Add an eviction mechanism for SDCH dictionaries.

net/base/sdch_observer.h

 // Copyright 2014 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_BASE_SDCH_OBSERVER_H_
 #define NET_BASE_SDCH_OBSERVER_H_
 
+#include <iosfwd>
+
 #include "net/base/net_export.h"
 
 class GURL;
 
 namespace net {
 
 class SdchManager;
 
 // Observer interface for SDCH.  Observers can register with
 // the SdchManager to receive notifications of various SDCH events.
 class NET_EXPORT SdchObserver {
  public:
   virtual ~SdchObserver();
 
-  // Notification that SDCH has seen a "Get-Dictionary" header.
+  // TODO(rdsmith): Add Added/Removed signals.  These are only needed if
+  // we end up with an implementation in which more than one observer
+  // generates Add/Removed events; otherwise, tracking can be done internally.
+
+  // TODO(rdsmith): Add signal that an Avail-Dictionary header was generated.
+  // Should be added if/when an observer wants to use it to fine-tune
+  // dictionary deprecation (e.g. if Avail-Dictionary is generated and
+  // the remote *doesn't* use it, that should deprecate the dictionary faster)
+
+  // A SDCH encoded response was received and the specified dictionary
+  // was used to decode it.  This notification only occurs for successful
+  // decodes.
+  // TODO(rdsmith): Should this notification indicate how much
+  // compression the dictionary provided?
+  virtual void OnDictionaryUsed(SdchManager* manager,
+                                const std::string& server_hash) = 0;
+
+  // A "Get-Dictionary" header has been seen.
   virtual void OnGetDictionary(SdchManager* manager,
                                const GURL& request_url,
                                const GURL& dictionary_url) = 0;
 
   // Notification that SDCH has received a request to clear all
   // its dictionaries.
   virtual void OnClearDictionaries(SdchManager* manager) = 0;
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_SDCH_MANAGER_H_