[WIP] ScreenManager: Add an external window mode

services/ui/display/screen_manager_ozone.h

Index: services/ui/display/screen_manager_ozone.h
diff --git a/services/ui/display/screen_manager_ozone.h b/services/ui/display/screen_manager_ozone.h
index a0d6aaaf7b90ae7b4122b9eaa1b2b0c5ba6d363e..c77d3462afa195318fca981a7018675651f32c81 100644
--- a/services/ui/display/screen_manager_ozone.h
+++ b/services/ui/display/screen_manager_ozone.h
@@ -48,7 +48,7 @@ class ScreenManagerOzone
 
   // ScreenManager:
   void AddInterfaces(service_manager::InterfaceRegistry* registry) override;
-  void Init(ScreenManagerDelegate* delegate) override;
+  void Init(ScreenManagerDelegate* delegate, WindowMode window_mode) override;
   void RequestCloseDisplay(int64_t display_id) override;

[kylechar, 2017/01/25 13:04:48]

I don't think this is the right thing to do. ScreenManagerOzone is perhaps
poorly named and it should be ScreenManagerChromeOS or ScreenManagerInternal but
it's built for Chrome OS. It will only work for internal window mode and it
controls the size of root drawable surfaces. For external window mode
ScreenManager doesn't control the root drawable surfaces, so there isn't much /
any code overlap.

ScreenManagerOzone won't compile if target_os != "chromeos". I think you'll need
to write a different ScreenManager implementation for external window mode or
maybe you can use ScreenManagerStub for now. 

The bulk of the work to get external window mode working is the WS. Right now
each ws::Display corresponds to a root drawable surface. The ws::Display has a
ws::PlatformDisplay (which again isn't well named) which is basically what
allows you to draw to a surface, it owns the ui::PlatformWindow and
ws::FrameGenerator. The WS needs to be changed so that ws::Display doesn't own a
ws::PlatformDisplay. The top level Chrome ServerWindows need to own
ws::PlatformDisplay, which I guess means that a ServerWindow owns the
ws::PlatformDisplay in both external and internal window mode.

   int64_t GetPrimaryDisplayId() const override;