Revert of Remove void** from disk_cache interface.

net/disk_cache/simple/simple_backend_impl.h

Index: net/disk_cache/simple/simple_backend_impl.h
diff --git a/net/disk_cache/simple/simple_backend_impl.h b/net/disk_cache/simple/simple_backend_impl.h
index 48c422f9f8802dc9bf837d0d75a01aab5d79c224..907ee5a6d4535cd03046014a9ee4e0b91afd9e51 100644
--- a/net/disk_cache/simple/simple_backend_impl.h
+++ b/net/disk_cache/simple/simple_backend_impl.h
@@ -13,6 +13,7 @@
 #include "base/compiler_specific.h"
 #include "base/containers/hash_tables.h"
 #include "base/files/file_path.h"
+#include "base/id_map.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
@@ -33,11 +34,6 @@
 // SimpleBackendImpl is a new cache backend that stores entries in individual
 // files.
 // See http://www.chromium.org/developers/design-documents/network-stack/disk-cache/very-simple-backend
-//
-// The SimpleBackendImpl provides safe iteration; mutating entries during
-// iteration cannot cause a crash. It is undefined whether entries created or
-// destroyed during the iteration will be included in any pre-existing
-// iterations.
 //
 // The non-static functions below must be called on the IO thread unless
 // otherwise stated.
@@ -102,16 +98,17 @@
                                  const CompletionCallback& callback) OVERRIDE;
   virtual int DoomEntriesSince(base::Time initial_time,
                                const CompletionCallback& callback) OVERRIDE;
-  virtual scoped_ptr<Iterator> CreateIterator() OVERRIDE;
+  virtual int OpenNextEntry(void** iter, Entry** next_entry,
+                            const CompletionCallback& callback) OVERRIDE;
+  virtual void EndEnumeration(void** iter) OVERRIDE;
   virtual void GetStats(
       std::vector<std::pair<std::string, std::string> >* stats) OVERRIDE;
   virtual void OnExternalCacheHit(const std::string& key) OVERRIDE;
 
  private:
-  class SimpleIterator;
-  friend class SimpleIterator;
-
   typedef base::hash_map<uint64, SimpleEntryImpl*> EntryMap;
+
+  typedef IDMap<std::vector<uint64>, IDMapOwnPointer> ActiveEnumerationMap;
 
   typedef base::Callback<void(base::Time mtime, uint64 max_size, int result)>
       InitializeIndexCallback;
@@ -127,6 +124,17 @@
     int net_error;
   };
 
+  // Convert an iterator from OpenNextEntry() to the key type for
+  // ActiveEnumerationMap. Note it takes a void** argument; this is for safety;
+  // if it took a void*, that would be type compatible with a void** permitting
+  // easy calls missing the dereference.
+  static ActiveEnumerationMap::KeyType IteratorToEnumerationId(void** iter);
+
+  // Convert a key from ActiveEnumerationMap back to a void*, suitable for
+  // storing in the iterator argument to OpenNextEntry().
+  static void* EnumerationIdToIterator(
+      ActiveEnumerationMap::KeyType enumeration_id);
+
   void InitializeIndex(const CompletionCallback& callback,
                        const DiskStatResult& result);
 
@@ -160,6 +168,14 @@
   // pending doom. This function does not block if there is an active entry,
   // which is very important to prevent races in DoomEntries() above.
   int DoomEntryFromHash(uint64 entry_hash, const CompletionCallback & callback);
+
+  // Called when the index is initilized to find the next entry in the iterator
+  // |iter|. If there are no more hashes in the iterator list, net::ERR_FAILED
+  // is returned. Otherwise, calls OpenEntryFromHash.
+  void GetNextEntryInIterator(void** iter,
+                              Entry** next_entry,
+                              const CompletionCallback& callback,
+                              int error_code);
 
   // Called when we tried to open an entry with hash alone. When a blank entry
   // has been created and filled in with information from the disk - based on a
@@ -179,6 +195,14 @@
                             const CompletionCallback& callback,
                             int error_code);
 
+  // Called at the end of the asynchronous operation triggered by
+  // OpenEntryFromHash. Makes sure to continue iterating if the open entry was
+  // not a success.
+  void CheckIterationReturnValue(void** iter,
+                                 Entry** entry,
+                                 const CompletionCallback& callback,
+                                 int error_code);
+
   // A callback thunk used by DoomEntries to clear the |entries_pending_doom_|
   // after a mass doom.
   void DoomEntriesComplete(scoped_ptr<std::vector<uint64> > entry_hashes,
@@ -196,6 +220,9 @@
 
   EntryMap active_entries_;
 
+  // One entry for every enumeration in progress.
+  ActiveEnumerationMap active_enumerations_;
+
   // The set of all entries which are currently being doomed. To avoid races,
   // these entries cannot have Doom/Create/Open operations run until the doom
   // is complete. The base::Closure map target is used to store deferred