mash: make Env::last_mouse_location() accurate for Mus

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 e1325b7842613f20e84d97d5c87dbdbadd4ef18c..9732917574ed6be64d8001f56fd49ee9ce112072 100644
--- a/ui/aura/test/aura_test_base.cc
+++ b/ui/aura/test/aura_test_base.cc
@@ -249,5 +249,14 @@ void AuraTestBaseWithType::SetUp() {
   AuraTestBase::SetUp();
 }
 
+AuraTestBaseMus::AuraTestBaseMus() {}
+
+AuraTestBaseMus::~AuraTestBaseMus() {}
+
+void AuraTestBaseMus::SetUp() {
+  ConfigureBackend(test::BackendType::MUS);
+  AuraTestBase::SetUp();
+}
+
 }  // namespace test
 }  // namespace aura