Add support code to test the cast system tray item.

ash/system/cast/tray_cast.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 ASH_SYSTEM_CAST_TRAY_CAST_H_
 #define ASH_SYSTEM_CAST_TRAY_CAST_H_
 
 #include "ash/cast_config_delegate.h"
 #include "ash/shell_observer.h"
 #include "ash/system/tray/system_tray_item.h"
 #include "base/memory/weak_ptr.h"
 
 namespace ash {
 namespace tray {
 class CastTrayView;
 class CastSelectDefaultView;
 class CastDetailedView;
 class CastDuplexView;
 }  // namespace tray
 
-class TrayCast : public SystemTrayItem, public ShellObserver {
+class ASH_EXPORT TrayCast : public SystemTrayItem, public ShellObserver {
  public:
   explicit TrayCast(SystemTray* system_tray);
   ~TrayCast() override;
 
  private:
+  // Helper/utility methods for testing.
+  friend class TrayCastTestAPI;
+  void StartCastForTest(const std::string& receiver_id);
+  void StopCastForTest();
+  enum ChildViewIds { TRAY_VIEW, SELECT_VIEW, CAST_VIEW };
+
   // Overridden from SystemTrayItem.
   views::View* CreateTrayView(user::LoginStatus status) override;
   views::View* CreateDefaultView(user::LoginStatus status) override;
   views::View* CreateDetailedView(user::LoginStatus status) override;
   void DestroyTrayView() override;
   void DestroyDefaultView() override;
   void DestroyDetailedView() override;
   void UpdateAfterShelfAlignmentChange(ShelfAlignment alignment) override;
 
   // Overridden from ShellObserver.
@@ skipping 23 matching lines @@
   bool has_cast_receivers_ = false;
   bool is_casting_ = false;
   base::WeakPtrFactory<TrayCast> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(TrayCast);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_CAST_TRAY_CAST_H_