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

chromecast/graphics/cast_window_manager.h

Index: chromecast/graphics/cast_window_manager.h
diff --git a/chromecast/graphics/cast_window_manager.h b/chromecast/graphics/cast_window_manager.h
index bf2dc4b63f3a292c79bd76465b361db176441208..2302c48944d547e09fad92a6564383e1526265fc 100644
--- a/chromecast/graphics/cast_window_manager.h
+++ b/chromecast/graphics/cast_window_manager.h
@@ -18,6 +18,17 @@ namespace chromecast {
 // 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);