Revert of Convert //net and //chromecast to std::unordered_*

net/disk_cache/memory/mem_backend_impl.h

Index: net/disk_cache/memory/mem_backend_impl.h
diff --git a/net/disk_cache/memory/mem_backend_impl.h b/net/disk_cache/memory/mem_backend_impl.h
index 60c7dc5d92200472bd39e85b4e9d5a5db2d86fb3..8abcca5b7a29e156b8f8c265050d073100a2c236 100644
--- a/net/disk_cache/memory/mem_backend_impl.h
+++ b/net/disk_cache/memory/mem_backend_impl.h
@@ -10,9 +10,9 @@
 #include <stdint.h>
 
 #include <string>
-#include <unordered_map>
 
 #include "base/compiler_specific.h"
+#include "base/containers/hash_tables.h"
 #include "base/containers/linked_list.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
@@ -97,7 +97,7 @@
   class MemIterator;
   friend class MemIterator;
 
-  using EntryMap = std::unordered_map<std::string, MemEntryImpl*>;
+  typedef base::hash_map<std::string, MemEntryImpl*> EntryMap;
 
   // Deletes entries from the cache until the current size is below the limit.
   void EvictIfNeeded();