Add an eviction mechanism for SDCH dictionaries.

net/base/sdch_observer.h

Index: net/base/sdch_observer.h
diff --git a/net/base/sdch_observer.h b/net/base/sdch_observer.h
index 2c5987d8698cb86f6206454ab0ff593854f437e7..6484dec196978c41e5a5f0bf57a7277433c86a41 100644
--- a/net/base/sdch_observer.h
+++ b/net/base/sdch_observer.h
@@ -5,6 +5,8 @@
 #ifndef NET_BASE_SDCH_OBSERVER_H_
 #define NET_BASE_SDCH_OBSERVER_H_
 
+#include <iosfwd>
+
 #include "net/base/net_export.h"
 
 class GURL;
@@ -19,7 +21,24 @@ 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;