Makes InputMethodMus deal with no connection

ui/aura/mus/window_tree_host_mus.h

 // Copyright 2015 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.
 
 #ifndef UI_AURA_MUS_WINDOW_TREE_HOST_MUS_H_
 #define UI_AURA_MUS_WINDOW_TREE_HOST_MUS_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 14 matching lines @@
 
 class InputMethodMus;
 class WindowPortMus;
 class WindowTreeClient;
 class WindowTreeHostMusDelegate;
 
 class AURA_EXPORT WindowTreeHostMus : public aura::WindowTreeHostPlatform {
  public:
   WindowTreeHostMus(
       std::unique_ptr<WindowPortMus> window_port,
-      WindowTreeHostMusDelegate* delegate,
+      WindowTreeClient* window_tree_client,
       int64_t display_id,
       const std::map<std::string, std::vector<uint8_t>>* properties = nullptr);
-  WindowTreeHostMus(
+  explicit WindowTreeHostMus(
       WindowTreeClient* window_tree_client,
       const std::map<std::string, std::vector<uint8_t>>* properties = nullptr);
 
   ~WindowTreeHostMus() override;
 
   // Sets the bounds in dips.
   void SetBoundsFromServer(const gfx::Rect& bounds);
 
   ui::EventDispatchDetails SendEventToProcessor(ui::Event* event) {
     return aura::WindowTreeHostPlatform::SendEventToProcessor(event);
@@ skipping 31 matching lines @@
   bool in_set_bounds_from_server_ = false;
 
   std::unique_ptr<InputMethodMus> input_method_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowTreeHostMus);
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_MUS_WINDOW_TREE_HOST_MUS_H_