Install FakeContextFactory for AuraMusWmTestBase

ui/aura/test/aura_mus_test_base.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/aura/test/aura_mus_test_base.h"
 
 namespace aura {
 namespace test {
 
 AuraMusWmTestBase::AuraMusWmTestBase() {}
 
 AuraMusWmTestBase::~AuraMusWmTestBase() {}
 
 void AuraMusWmTestBase::SetUp() {
+  // Run AuraTestBase::SetUp() first because it puts an InProcessContextFactory
+  // in env.
   EnableMusWithTestWindowTree();
   AuraTestBase::SetUp();
+
+  aura::Env* env = aura::Env::GetInstance();
+  DCHECK(env);
+  context_factory_to_restore_ = env->context_factory();
+  env->set_context_factory(&context_factory_);
+}
+
+void AuraMusWmTestBase::TearDown() {
+  aura::Env::GetInstance()->set_context_factory(context_factory_to_restore_);
+  AuraTestBase::TearDown();
 }
 
 AuraMusClientTestBase::AuraMusClientTestBase() {}
 
 AuraMusClientTestBase::~AuraMusClientTestBase() {}
 
 void AuraMusClientTestBase::SetUp() {
+  // Run AuraTestBase::SetUp() first because it puts an InProcessContextFactory
+  // in env.
   EnableMusWithTestWindowTree();
   set_window_manager_delegate(nullptr);
   AuraTestBase::SetUp();
+
+  aura::Env* env = aura::Env::GetInstance();
+  DCHECK(env);
+  context_factory_to_restore_ = env->context_factory();
+  env->set_context_factory(&context_factory_);
+}
+
+void AuraMusClientTestBase::TearDown() {
+  aura::Env::GetInstance()->set_context_factory(context_factory_to_restore_);
+  AuraTestBase::TearDown();
 }
 
 }  // namespace test
 }  // namespace aura