Adds DesktopWindowTreeHostMus

ui/aura/test/aura_test_helper.h

Index: ui/aura/test/aura_test_helper.h
diff --git a/ui/aura/test/aura_test_helper.h b/ui/aura/test/aura_test_helper.h
index c04f52c32ac7904690eb6a0f2c12d7ba49875635..2906973936ea42ee2d07500c008992af96c1d0a6 100644
--- a/ui/aura/test/aura_test_helper.h
+++ b/ui/aura/test/aura_test_helper.h
@@ -53,8 +53,15 @@ class AuraTestHelper {
   explicit AuraTestHelper(base::MessageLoopForUI* message_loop);
   ~AuraTestHelper();
 
-  void EnableMus(WindowTreeClientDelegate* window_tree_delegate,
-                 WindowManagerDelegate* window_manager_delegate);
+  // Makes aura target mus with a mock WindowTree (TestWindowTree). Must be
+  // called before SetUp().
+  void EnableMusWithTestWindowTree(
+      WindowTreeClientDelegate* window_tree_delegate,
+      WindowManagerDelegate* window_manager_delegate);
+
+  // Makes aura target mus with the specified WindowTreeClient. Must be called
+  // before SetUp().
+  void EnableMusWithWindowTreeClient(WindowTreeClient* window_tree_client);
 
   // Creates and initializes (shows and sizes) the RootWindow for use in tests.
   void SetUp(ui::ContextFactory* context_factory);
@@ -72,19 +79,39 @@ class AuraTestHelper {
 
   TestScreen* test_screen() { return test_screen_.get(); }
 
+  // This function only returns a valid value if EnableMusWithTestWindowTree()
+  // was called.
   TestWindowTree* window_tree();
+
+  // Returns a WindowTreeClient only if one of the EnableMus functions is
+  // called.
   WindowTreeClient* window_tree_client();
 
   client::FocusClient* focus_client() { return focus_client_.get(); }
   client::CaptureClient* capture_client();
 
  private:
-  Env::WindowPortFactory InitMus();
+  enum class Mode {
+    // Classic aura.
+    LOCAL,
+
+    // Mus with a test WindowTree implementation that does not target the real
+    // service:ui.
+    MUS_CREATE_WINDOW_TREE_CLIENT,
 
-  std::unique_ptr<WindowPort> CreateWindowPortMus(Window* window);
+    // Mus without creating a WindowTree. This is used when the test wants to
+    // create the WindowTreeClient itself. This mode is enabled by way of
+    // EnableMusWithWindowTreeClient().
+    MUS,
+  };
 
-  base::MessageLoopForUI* message_loop_;
-  bool use_mus_ = false;
+  // Initializes a WindowTreeClient with a test WindowTree.
+  void InitWindowTreeClient();
+
+  // Factory function for creating the appropriate WindowPort function.
+  std::unique_ptr<WindowPort> CreateWindowPort(Window* window);
+
+  Mode mode_ = Mode::LOCAL;
   bool setup_called_;
   bool teardown_called_;
   std::unique_ptr<TestWindowTreeClientSetup> window_tree_client_setup_;
@@ -99,6 +126,8 @@ class AuraTestHelper {
   WindowTreeClientDelegate* window_tree_delegate_ = nullptr;
   WindowManagerDelegate* window_manager_delegate_ = nullptr;
 
+  WindowTreeClient* window_tree_client_ = nullptr;
+
   DISALLOW_COPY_AND_ASSIGN(AuraTestHelper);
 };