Provide skeleton functionality for AppCache handling in the network service.

content/browser/appcache/appcache_job.cc

Index: content/browser/appcache/appcache_job.cc
diff --git a/content/browser/appcache/appcache_job.cc b/content/browser/appcache/appcache_job.cc
index 0666c926811dbdb7047fb8e0fbef6f4d09854e37..27a5897298f9aef2f51c2c5714d95333554a012a 100644
--- a/content/browser/appcache/appcache_job.cc
+++ b/content/browser/appcache/appcache_job.cc
@@ -42,6 +42,10 @@ net::URLRequestJob* AppCacheJob::AsURLRequestJob() {
   return nullptr;
 }
 
+AppCacheURLLoaderJob* AppCacheJob::AsURLLoaderJob() {
+  return nullptr;
+}
+
 AppCacheJob::AppCacheJob() : weak_factory_(this) {}
 
 }  // namespace content