Primary display change notifications.

services/ui/display/platform_screen_delegate.h

Index: services/ui/display/platform_screen_delegate.h
diff --git a/services/ui/display/platform_screen_delegate.h b/services/ui/display/platform_screen_delegate.h
index b326c6a14b7ec7c9f0d1d01c6e4a1c6152b27822..3a504aa196536f68ac231cc3fe6db43eaed8c47d 100644
--- a/services/ui/display/platform_screen_delegate.h
+++ b/services/ui/display/platform_screen_delegate.h
@@ -34,6 +34,11 @@ class PlatformScreenDelegate {
   virtual void OnDisplayModified(int64_t id,
                                  const ViewportMetrics& metrics) = 0;
 
+  // Called when the primary display is changed. If the last display is about
+  // to be removed then |primary_display_id| will be set to kInvalidDisplayID

[sky, 2016/10/28 17:08:47]

Is it necessary that OnPrimaryDisplayChanged() is sent in the case of a removal
of the last display? That seems mildly confusing and would think the
OnDisplayRemoved of the last display implies there is no primary display.

[kylechar, 2016/10/28 19:40:36]

Not necessary to do it one way or the other. Changed.

+  // to indicate there is no primary display.
+  virtual void OnPrimaryDisplayChanged(int64_t primary_display_id) = 0;
+
  protected:
   virtual ~PlatformScreenDelegate() {}
 };