Remove disk_cache::BackendImpl::OpenPrevEntry() and all users.

net/disk_cache/blockfile/in_flight_backend_io.h

Index: net/disk_cache/blockfile/in_flight_backend_io.h
diff --git a/net/disk_cache/blockfile/in_flight_backend_io.h b/net/disk_cache/blockfile/in_flight_backend_io.h
index 935d3a5f9f249281641fa6b0eb5526ffa9a16bee..76557d16abccb71caaabdf9b41f7e463e5a50079 100644
--- a/net/disk_cache/blockfile/in_flight_backend_io.h
+++ b/net/disk_cache/blockfile/in_flight_backend_io.h
@@ -56,7 +56,6 @@ class BackendIO : public BackgroundIO {
                           const base::Time end_time);
   void DoomEntriesSince(const base::Time initial_time);
   void OpenNextEntry(void** iter, Entry** next_entry);
-  void OpenPrevEntry(void** iter, Entry** prev_entry);
   void EndEnumeration(void* iterator);
   void OnExternalCacheHit(const std::string& key);
   void CloseEntryImpl(EntryImpl* entry);
@@ -91,7 +90,6 @@ class BackendIO : public BackgroundIO {
     OP_DOOM_BETWEEN,
     OP_DOOM_SINCE,
     OP_OPEN_NEXT,
-    OP_OPEN_PREV,
     OP_END_ENUMERATION,
     OP_ON_EXTERNAL_CACHE_HIT,
     OP_CLOSE_ENTRY,
@@ -168,8 +166,6 @@ class InFlightBackendIO : public InFlightIO {
                         const net::CompletionCallback& callback);
   void OpenNextEntry(void** iter, Entry** next_entry,
                      const net::CompletionCallback& callback);
-  void OpenPrevEntry(void** iter, Entry** prev_entry,
-                     const net::CompletionCallback& callback);
   void EndEnumeration(void* iterator);
   void OnExternalCacheHit(const std::string& key);
   void CloseEntryImpl(EntryImpl* entry);