Http cache: Add support for a dedicated cache thread.

net/http/http_cache.cc

Index: net/http/http_cache.cc
===================================================================
--- net/http/http_cache.cc	(revision 45869)
+++ net/http/http_cache.cc	(working copy)
@@ -201,8 +201,10 @@
                      SSLConfigService* ssl_config_service,
                      HttpAuthHandlerFactory* http_auth_handler_factory,
                      const FilePath& cache_dir,
+                     MessageLoop* cache_thread,
                      int cache_size)
     : disk_cache_dir_(cache_dir),
+      cache_thread_(cache_thread),
       mode_(NORMAL),
       type_(DISK_CACHE),
       network_layer_(HttpNetworkLayer::CreateFactory(
@@ -215,8 +217,10 @@
 
 HttpCache::HttpCache(HttpNetworkSession* session,
                      const FilePath& cache_dir,
+                     MessageLoop* cache_thread,
                      int cache_size)
     : disk_cache_dir_(cache_dir),
+      cache_thread_(cache_thread),
       mode_(NORMAL),
       type_(DISK_CACHE),
       network_layer_(HttpNetworkLayer::CreateFactory(session)),
@@ -289,6 +293,13 @@
   return disk_cache_.get();
 }
 
+int HttpCache::GetBackend(disk_cache::Backend** backend,
+                          CompletionCallback* callback) {
+  DCHECK(callback != NULL);
+  *backend = GetBackend();
+  return OK;
+}
+
 int HttpCache::CreateTransaction(scoped_ptr<HttpTransaction>* trans) {
   // Do lazy initialization of disk cache if needed.
   GetBackend();