[Aura] Support always-on-top top level window.

ui/aura/test/aura_test_base.cc

Index: ui/aura/test/aura_test_base.cc
diff --git a/ui/aura/test/aura_test_base.cc b/ui/aura/test/aura_test_base.cc
index 8d7a7bcfb3abfc93dbc589731d278fcfb40455ad..4cd94b8730562ac9408a664e80eecce3c51c1504 100644
--- a/ui/aura/test/aura_test_base.cc
+++ b/ui/aura/test/aura_test_base.cc
@@ -38,8 +38,7 @@ AuraTestBase::~AuraTestBase() {
 
   // Flush the message loop because we have pending release tasks
   // and these tasks if un-executed would upset Valgrind.
-  message_loop_.RunAllPendingWithDispatcher(
-      Desktop::GetInstance()->GetDispatcher());
+  FlushMessageLoop();
 
   // Ensure that we don't use the previously-allocated static Desktop object
   // later -- on Linux, it holds a reference to our message loop's X connection.
@@ -61,5 +60,10 @@ void AuraTestBase::TearDown() {
   testing::Test::TearDown();
 }
 
+void AuraTestBase::FlushMessageLoop() {
+  message_loop_.RunAllPendingWithDispatcher(
+      Desktop::GetInstance()->GetDispatcher());
+}
+
 }  // namespace test
 }  // namespace aura