Reland r113263 rebased after revert of r113249.

net/disk_cache/disk_cache.h

Index: net/disk_cache/disk_cache.h
diff --git a/net/disk_cache/disk_cache.h b/net/disk_cache/disk_cache.h
index d220d910ed7cf29ece1a4b1e8137dee4653f0f00..3f52e23b6bb33cc3924f82edf4f97070392f242f 100644
--- a/net/disk_cache/disk_cache.h
+++ b/net/disk_cache/disk_cache.h
@@ -131,6 +131,8 @@ class NET_EXPORT Backend {
   // therefore it does not impact the eviction ranking of the entry.
   virtual int OpenNextEntry(void** iter, Entry** next_entry,
                             OldCompletionCallback* callback) = 0;
+  virtual int OpenNextEntry(void** iter, Entry** next_entry,
+                            const net::CompletionCallback& callback) = 0;
 
   // Releases iter without returning the next entry. Whenever OpenNextEntry()
   // returns true, but the caller is not interested in continuing the