Move kInvalidDisplayID to display_constants.h.

ui/message_center/views/desktop_popup_alignment_delegate.cc

Index: ui/message_center/views/desktop_popup_alignment_delegate.cc
diff --git a/ui/message_center/views/desktop_popup_alignment_delegate.cc b/ui/message_center/views/desktop_popup_alignment_delegate.cc
index 1c32a1eb1e22e69208aebd3f92141faf861d5592..7351661ce07e838f886fe7689659096d54f3ce90 100644
--- a/ui/message_center/views/desktop_popup_alignment_delegate.cc
+++ b/ui/message_center/views/desktop_popup_alignment_delegate.cc
@@ -14,7 +14,7 @@ namespace message_center {
 
 DesktopPopupAlignmentDelegate::DesktopPopupAlignmentDelegate()
     : alignment_(POPUP_ALIGNMENT_BOTTOM | POPUP_ALIGNMENT_RIGHT),
-      primary_display_id_(display::Display::kInvalidDisplayID),
+      primary_display_id_(display::kInvalidDisplayID),
       screen_(NULL) {}
 
 DesktopPopupAlignmentDelegate::~DesktopPopupAlignmentDelegate() {
@@ -121,7 +121,7 @@ void DesktopPopupAlignmentDelegate::OnDisplayMetricsChanged(
     uint32_t metrics) {
   // Set to kInvalidDisplayID so the alignment is updated regardless of whether
   // the primary display actually changed.
-  primary_display_id_ = display::Display::kInvalidDisplayID;
+  primary_display_id_ = display::kInvalidDisplayID;
   UpdatePrimaryDisplay();
 }