Replace ancient crufty AppCacheThread with much improved MessageLoopProxy usage.

webkit/appcache/appcache_storage_impl.h

Index: webkit/appcache/appcache_storage_impl.h
===================================================================
--- webkit/appcache/appcache_storage_impl.h	(revision 100467)
+++ webkit/appcache/appcache_storage_impl.h	(working copy)
@@ -25,6 +25,7 @@
   virtual ~AppCacheStorageImpl();
 
   void Initialize(const FilePath& cache_directory,
+                  base::MessageLoopProxy* db_thread,
                   base::MessageLoopProxy* cache_thread);
   void Disable();
   bool is_disabled() const { return is_disabled_; }
@@ -122,9 +123,14 @@
 
   // The directory in which we place files in the file system.
   FilePath cache_directory_;
-  scoped_refptr<base::MessageLoopProxy> cache_thread_;
   bool is_incognito_;
 
+  // This class operates primarily on the io thread, but schedules
+  // its DatabaseTasks on the db thread. Seperately, the disk_cache uses
+  // the cache_thread.
+  scoped_refptr<base::MessageLoopProxy> db_thread_;
+  scoped_refptr<base::MessageLoopProxy> cache_thread_;
+
   // Structures to keep track of DatabaseTasks that are in-flight.
   DatabaseTaskQueue scheduled_database_tasks_;
   PendingCacheLoads pending_cache_loads_;