Have PlatformScreen use DisplayConfigurator.

services/ui/ws/platform_screen.h

Index: services/ui/ws/platform_screen.h
diff --git a/services/ui/ws/platform_screen.h b/services/ui/ws/platform_screen.h
index 3ed27930186b397f0a0d474e16d212e87e892be8..075dc2596a77cfa9b84fbd317679ba3af45a0242 100644
--- a/services/ui/ws/platform_screen.h
+++ b/services/ui/ws/platform_screen.h
@@ -20,6 +20,9 @@ namespace ws {
 // attached physical displays.
 class PlatformScreen {
  public:
+  using ConfiguredDisplayCallback =
+      base::Callback<void(int64_t, const gfx::Rect&)>;
+
   virtual ~PlatformScreen() {}
 
   // Creates a PlatformScreen instance.
@@ -28,9 +31,6 @@ class PlatformScreen {
   // Initializes platform specific screen resources.
   virtual void Init() = 0;
 
-  using ConfiguredDisplayCallback =
-      base::Callback<void(int64_t, const gfx::Rect&)>;
-
   // ConfigurePhysicalDisplay() configures a single physical display and returns
   // its id and bounds for it via |callback|.
   virtual void ConfigurePhysicalDisplay(