Fix implicit scoped_refptr<T> to T* conversion in TestMetroViewerProcessHost

ash/test/test_metro_viewer_process_host.h

Index: ash/test/test_metro_viewer_process_host.h
diff --git a/ash/test/test_metro_viewer_process_host.h b/ash/test/test_metro_viewer_process_host.h
index 95709aecd35a147a5f05ef5984911d136c7c9f65..bb39351533fbf1aaca802abaf254458fffb78369 100644
--- a/ash/test/test_metro_viewer_process_host.h
+++ b/ash/test/test_metro_viewer_process_host.h
@@ -15,7 +15,8 @@ namespace test {
 
 class TestMetroViewerProcessHost : public win8::MetroViewerProcessHost {
  public:
-  TestMetroViewerProcessHost(base::SingleThreadTaskRunner* ipc_task_runner);
+  TestMetroViewerProcessHost(
+      const scoped_refptr<base::SingleThreadTaskRunner>& ipc_task_runner);
   virtual ~TestMetroViewerProcessHost();
 
   bool closed_unexpectedly() { return closed_unexpectedly_; }