Fix window/display bounds with multiple windows in mus.

services/ui/display/platform_screen_impl.h

Index: services/ui/display/platform_screen_impl.h
diff --git a/services/ui/display/platform_screen_impl.h b/services/ui/display/platform_screen_impl.h
index 1bf5c469f456e6034079a1577f9907d13d81e096..0b5ff5a8879348320be9246913112c84207731f1 100644
--- a/services/ui/display/platform_screen_impl.h
+++ b/services/ui/display/platform_screen_impl.h
@@ -24,6 +24,7 @@ class PlatformScreenImpl : public PlatformScreen {
   void Init() override;
   void ConfigurePhysicalDisplay(
       const PlatformScreen::ConfiguredDisplayCallback& callback) override;
+  int64_t GetPrimaryDisplayId() const override;
 
   DISALLOW_COPY_AND_ASSIGN(PlatformScreenImpl);
 };