Makes sure bounds and visibilty are updated correctly for new displays

ui/aura/test/aura_test_base.h

Index: ui/aura/test/aura_test_base.h
diff --git a/ui/aura/test/aura_test_base.h b/ui/aura/test/aura_test_base.h
index df5d4a818ccda9a237e59c4d68206e8184c8f756..1623b0a330a8fea8db04198f17e63fadd69a75f2 100644
--- a/ui/aura/test/aura_test_base.h
+++ b/ui/aura/test/aura_test_base.h
@@ -5,6 +5,9 @@
 #ifndef UI_AURA_TEST_AURA_TEST_BASE_H_
 #define UI_AURA_TEST_AURA_TEST_BASE_H_
 
+#include <memory>
+#include <vector>
+
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/message_loop/message_loop.h"
@@ -129,7 +132,7 @@ class AuraTestBase : public testing::Test,
   base::MessageLoopForUI message_loop_;
   PropertyConverter property_converter_;
   std::unique_ptr<AuraTestHelper> helper_;
-  std::unique_ptr<WindowTreeHostMus> window_tree_host_mus_;
+  std::vector<std::unique_ptr<WindowTreeHostMus>> window_tree_hosts_;
 
   DISALLOW_COPY_AND_ASSIGN(AuraTestBase);
 };