[Chromecast] Add support for z-order and window focus.

chromecast/graphics/cast_window_manager.h

 // Copyright 2017 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 CHROMECAST_GRAPHICS_CAST_WINDOW_MANAGER_H_
 #define CHROMECAST_GRAPHICS_CAST_WINDOW_MANAGER_H_
 
 #include <memory>
 
 #include "base/macros.h"
 #include "ui/gfx/native_widget_types.h"
 
 namespace chromecast {
 
 // Chromecast's window-manager interface.
 // This declares the interface to add top-level windows to the Chromecast
 // platform window.  It is owned by the UI thread, and generally one instance
 // should exist per platform root window (e.g., in Ozone, one per Ozone window).
 class CastWindowManager {
  public:
+  // Note: these window IDs are ordered by z-order.
+  enum WindowId {
+    BOTTOM = -1,
+    APP = BOTTOM,
+    DEBUG_OVERLAY,
+    INFO_OVERLAY,
+    SOFT_KEYBOARD,
+    VOLUME,
+    TOP = VOLUME
+  };
+
   // Creates the platform-specific CastWindowManager.
   static std::unique_ptr<CastWindowManager> Create(bool enable_input);
 
   virtual ~CastWindowManager() {}
 
   // Remove all windows and release all graphics resources.
   // Can be called multiple times.
   virtual void TearDown() = 0;
 
   // Adds a window to the window manager.
   // This doesn't necessarily make the window visible.
   // If the window manager hasn't been initialized, this has the side effect of
   // causing it to initialize.
   virtual void AddWindow(gfx::NativeView window) = 0;
 };
 
 }  // namespace chromecast
 
 #endif  // CHROMECAST_GRAPHICS_CAST_WINDOW_MANAGER_H_