AppCache: Use a dedicated thread for the disk cache.

webkit/appcache/appcache_disk_cache.h

Index: webkit/appcache/appcache_disk_cache.h
===================================================================
--- webkit/appcache/appcache_disk_cache.h	(revision 48989)
+++ webkit/appcache/appcache_disk_cache.h	(working copy)
@@ -29,6 +29,7 @@
   // Initializes the object to use disk backed storage.
   int InitWithDiskBackend(const FilePath& disk_cache_directory,
                           int disk_cache_size, bool force,
+                          base::MessageLoopProxy* cache_thread,
                           net::CompletionCallback* callback);
 
   // Initializes the object to use memory only storage.
@@ -85,7 +86,8 @@
     return create_backend_callback_.get() != NULL;
   }
   int Init(net::CacheType cache_type, const FilePath& directory,
-           int cache_size, bool force, net::CompletionCallback* callback);
+           int cache_size, bool force, base::MessageLoopProxy* cache_thread,
+           net::CompletionCallback* callback);
   void OnCreateBackendComplete(int rv);
 
   bool is_disabled_;