Pass root ServerWindow id to FrameGenerator.

services/ui/ws/ids.h

Index: services/ui/ws/ids.h
diff --git a/services/ui/ws/ids.h b/services/ui/ws/ids.h
index a6268349313afe6001f54a0121f83b5a8c8bcccd..773a03479412984a10f7871796033fd16a21f993 100644
--- a/services/ui/ws/ids.h
+++ b/services/ui/ws/ids.h
@@ -38,9 +38,9 @@ const ClientSpecificId kInvalidClientId = 0;
 // that embed roots use the client id in creating the window id to avoid
 // possible conflicts.
 struct WindowId {
-  WindowId(ClientSpecificId client_id, ClientSpecificId window_id)
+  constexpr WindowId(ClientSpecificId client_id, ClientSpecificId window_id)
       : client_id(client_id), window_id(window_id) {}
-  WindowId() : client_id(0), window_id(0) {}
+  constexpr WindowId() : client_id(0), window_id(0) {}
 
   bool operator==(const WindowId& other) const {
     return other.client_id == client_id && other.window_id == window_id;
@@ -98,7 +98,7 @@ inline WindowId RootWindowId(uint16_t index) {
 }  // namespace ws
 }  // namespace ui
 
-namespace BASE_HASH_NAMESPACE {
+namespace std {
 
 template <>
 struct hash<ui::ws::ClientWindowId> {
@@ -114,6 +114,6 @@ struct hash<ui::ws::WindowId> {
   }
 };
 
-}  // namespace BASE_HASH_NAMESPACE
+}  // namespace std
 
 #endif  // SERVICES_UI_WS_IDS_H_