reapply r70628. It was wrongly blamed for breaking Linux valgrind bots.

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 59efe0652fb529fbaaa5d2b9275709dab5d1d772..18dd4474fbf066663ac31dab3f90450b73ab2c56 100644
--- a/net/disk_cache/disk_cache.h
+++ b/net/disk_cache/disk_cache.h
@@ -25,6 +25,7 @@ class MessageLoopProxy;
 
 namespace net {
 class IOBuffer;
+class NetLog;
 }
 
 namespace disk_cache {
@@ -50,7 +51,8 @@ typedef net::CompletionCallback CompletionCallback;
 // completes (the callback is notified).
 int CreateCacheBackend(net::CacheType type, const FilePath& path, int max_bytes,
                        bool force, base::MessageLoopProxy* thread,
-                       Backend** backend, CompletionCallback* callback);
+                       net::NetLog* net_log, Backend** backend,
+                       CompletionCallback* callback);
 
 // The root interface for a disk cache instance.
 class Backend {