Unify display ids between Display and PlatformDisplay.

services/ui/ws/display_manager.cc

Index: services/ui/ws/display_manager.cc
diff --git a/services/ui/ws/display_manager.cc b/services/ui/ws/display_manager.cc
index fadbfe9a5510a604bbfb2be40e159cf51f732dfd..8f37fd9394bad147ee46681ad01fb3f5dbba6328 100644
--- a/services/ui/ws/display_manager.cc
+++ b/services/ui/ws/display_manager.cc
@@ -23,8 +23,7 @@ DisplayManager::DisplayManager(DisplayManagerDelegate* delegate,
     // 0 as invalid.
     : delegate_(delegate),
       user_id_tracker_(user_id_tracker),
-      next_root_id_(0),
-      next_display_id_(1) {
+      next_root_id_(0) {
   user_id_tracker_->AddObserver(this);
 }
 
@@ -129,13 +128,6 @@ WindowId DisplayManager::GetAndAdvanceNextRootId() {
   return RootWindowId(id);
 }
 
-uint32_t DisplayManager::GetAndAdvanceNextDisplayId() {
-  // TODO(sky): handle wrapping!
-  const uint32_t id = next_display_id_++;
-  DCHECK_LT(id, next_display_id_);
-  return id;
-}
-
 void DisplayManager::OnDisplayAcceleratedWidgetAvailable(Display* display) {
   DCHECK_NE(0u, pending_displays_.count(display));
   DCHECK_EQ(0u, displays_.count(display));