Install FakeContextFactory for AuraMusWmTestBase

ui/aura/test/aura_mus_test_base.h

Index: ui/aura/test/aura_mus_test_base.h
diff --git a/ui/aura/test/aura_mus_test_base.h b/ui/aura/test/aura_mus_test_base.h
index 8964dfbabbf7a7c39b5cd539d6181da77f1ca901..958583126f957e6d7dbc66d8f8e8f2ba1d895333 100644
--- a/ui/aura/test/aura_mus_test_base.h
+++ b/ui/aura/test/aura_mus_test_base.h
@@ -7,6 +7,7 @@
 
 #include "base/macros.h"
 #include "ui/aura/test/aura_test_base.h"
+#include "ui/compositor/test/fake_context_factory.h"
 
 namespace aura {
 namespace test {
@@ -23,8 +24,12 @@ class AuraMusWmTestBase : public AuraTestBase {
 
   // AuraTestBase:
   void SetUp() override;
+  void TearDown() override;
 
  private:
+  ui::FakeContextFactory context_factory_;
+  ui::ContextFactory* context_factory_to_restore_ = nullptr;
+
   DISALLOW_COPY_AND_ASSIGN(AuraMusWmTestBase);
 };