Create MetroViewerProcessHost as a common base for TestMetroViewerProcessHost and ChromeMetroViewer…

ash/test/ash_test_base.cc

Index: ash/test/ash_test_base.cc
diff --git a/ash/test/ash_test_base.cc b/ash/test/ash_test_base.cc
index 99105e18da3134cca377897b147b6775ff0b8ea0..87f2243b73f37195c0e4a4273e40a6678c6b0f67 100644
--- a/ash/test/ash_test_base.cc
+++ b/ash/test/ash_test_base.cc
@@ -119,7 +119,14 @@ void AshTestBase::SetUp() {
   if (base::win::GetVersion() >= base::win::VERSION_WIN8 &&
       !CommandLine::ForCurrentProcess()->HasSwitch(
           ash::switches::kForceAshToDesktop)) {
-    metro_viewer_host_.reset(new TestMetroViewerProcessHost("viewer"));
+    ipc_thread_.reset(new base::Thread("test_metro_viewer_ipc_thread"));
+    base::Thread::Options options;
+    options.message_loop_type = base::MessageLoop::TYPE_IO;
+    ipc_thread_->StartWithOptions(options);
+
+    metro_viewer_host_.reset(
+        new TestMetroViewerProcessHost("viewer",
+                                       ipc_thread_->message_loop_proxy()));
     CHECK(metro_viewer_host_->LaunchViewerAndWaitForConnection(
         win8::test::kDefaultTestAppUserModelId));
     aura::RemoteRootWindowHostWin* root_window_host =