Use override redirect window for unit tests
 This is how ash works on the device (no wm) and
eliminates flaky-ness caused by WM.

BUG=none
TEST=none

Review URL: https://chromiumcodereview.appspot.com/14698005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@200976 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/ash/test/ash_test_helper.cc b/ash/test/ash_test_helper.cc
index 4c7ac84..5015075 100644
--- a/ash/test/ash_test_helper.cc
+++ b/ash/test/ash_test_helper.cc
@@ -20,6 +20,10 @@
 #include "chromeos/power/power_manager_handler.h"
 #endif
 
+#if defined(USE_X11)
+#include "ui/aura/root_window_host_x11.h"
+#endif
+
 namespace ash {
 namespace test {
 
@@ -27,6 +31,9 @@
     : message_loop_(message_loop),
       test_shell_delegate_(NULL) {
   CHECK(message_loop_);
+#if defined(USE_X11)
+  aura::test::SetUseOverrideRedirectWindowByDefault(true);
+#endif
 }
 
 AshTestHelper::~AshTestHelper() {