[3/4][Ozone-Drm] Use numeric ID to map to callback

ui/ozone/platform/drm/gpu/drm_device.h

Index: ui/ozone/platform/drm/gpu/drm_device.h
diff --git a/ui/ozone/platform/drm/gpu/drm_device.h b/ui/ozone/platform/drm/gpu/drm_device.h
index 546311c5e59589a61b5edaf3fbc168a52782e878..fa9951231b31422ef07c1335a4b991ddf18ac6dc 100644
--- a/ui/ozone/platform/drm/gpu/drm_device.h
+++ b/ui/ozone/platform/drm/gpu/drm_device.h
@@ -177,6 +177,7 @@ class OZONE_EXPORT DrmDevice : public base::RefCountedThreadSafe<DrmDevice> {
 
  private:
   class IOWatcher;
+  class PageFlipManager;
 
   // Path to DRM device.
   const base::FilePath device_path_;
@@ -190,6 +191,8 @@ class OZONE_EXPORT DrmDevice : public base::RefCountedThreadSafe<DrmDevice> {
   // Watcher for |fd_| listening for page flip events.
   scoped_refptr<IOWatcher> watcher_;
 
+  scoped_refptr<PageFlipManager> page_flip_manager_;
+
   DISALLOW_COPY_AND_ASSIGN(DrmDevice);
 };