Primary display change notifications.

services/ui/public/interfaces/display_manager.mojom

Index: services/ui/public/interfaces/display_manager.mojom
diff --git a/services/ui/public/interfaces/display.mojom b/services/ui/public/interfaces/display_manager.mojom
similarity index 54%
rename from services/ui/public/interfaces/display.mojom
rename to services/ui/public/interfaces/display_manager.mojom
index 2c10ce8de90ead441d4c1a28e63de66cbf5369a7..bffc624d050ca47403d060dbae58b67127222678 100644
--- a/services/ui/public/interfaces/display.mojom
+++ b/services/ui/public/interfaces/display_manager.mojom
@@ -7,8 +7,14 @@ module ui.mojom;
 import "services/ui/public/interfaces/window_manager_constants.mojom";
 
 interface DisplayManagerObserver {
-  // Sent when the observer is added. Gives the initial state.
-  OnDisplays(array<WsDisplay> displays);
+  // Sent when the observer is added. |displays| will contain all known
+  // displays. If the system that WS is running on has an integrated display,
+  // for example a laptop internal display, then |internal_display_id| will
+  // be the corresponding dislay id. If there is no internal display then
+  // |internal_display_id| will be kInvalidDisplayID.
+  OnDisplays(array<WsDisplay> displays,
+             int64 primary_display_id,
+             int64 internal_display_id);
 
   // The specified set of displays has changed in some way. This is used both
   // when a new display is added, or when a property of a display changes.
@@ -17,7 +23,10 @@ interface DisplayManagerObserver {
   OnDisplaysChanged(array<WsDisplay> displays);
 
   // An existing display was removed.
-  OnDisplayRemoved(int64 id);
+  OnDisplayRemoved(int64 display_id);
+
+  // The primary display has changed.
+  OnPrimaryDisplayChanged(int64 primary_display_id);
 };
 
 interface DisplayManager {