Add mojom::DisplayController.

services/ui/display/platform_screen.h

Index: services/ui/display/platform_screen.h
diff --git a/services/ui/display/platform_screen.h b/services/ui/display/platform_screen.h
index b782ee7ce2a7de9d1cbf92cd4391f6b79bddd3fd..843944200f82362d5ef0c51e42b29cd661694590 100644
--- a/services/ui/display/platform_screen.h
+++ b/services/ui/display/platform_screen.h
@@ -7,6 +7,7 @@
 
 #include <memory>
 
+#include "base/macros.h"
 #include "services/ui/display/platform_screen_delegate.h"
 
 namespace display {
@@ -15,10 +16,12 @@ namespace display {
 // attached physical displays.
 class PlatformScreen {
  public:
-  virtual ~PlatformScreen() {}
+  PlatformScreen();
+  virtual ~PlatformScreen();
 
-  // Creates a PlatformScreen instance.
+  // Creates a singleton PlatformScreen instance that is owned by caller.

[sky, 2016/09/08 18:03:35]

'caller' -> 'the caller'.

optional: that this returns a unique_ptr implies it's owned, so consider nuking
that part of the comment.

[kylechar, 2016/09/08 18:12:03]

Done.

   static std::unique_ptr<PlatformScreen> Create();
+  static PlatformScreen* GetInstance();
 
   // Triggers initial display configuration to start. On device this will
   // configuration the connected displays. Off device this will create one or
@@ -28,6 +31,11 @@ class PlatformScreen {
   virtual void Init(PlatformScreenDelegate* delegate) = 0;
 
   virtual int64_t GetPrimaryDisplayId() const = 0;
+
+ private:
+  static PlatformScreen* instance_;  // Instance is not owned.
+
+  DISALLOW_COPY_AND_ASSIGN(PlatformScreen);
 };
 
 }  // namespace display