[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 6fc2e495bf9afa1ead66da524ef6270c79b04e8f..1e3d12e6ca9ddbfa946b930b6b5c352c87684066 100644
--- a/ui/ozone/platform/drm/gpu/drm_device.h
+++ b/ui/ozone/platform/drm/gpu/drm_device.h
@@ -179,6 +179,7 @@ class OZONE_EXPORT DrmDevice : public base::RefCountedThreadSafe<DrmDevice> {
 
  private:
   class IOWatcher;
+  class PageFlipManager;
 
   // Path to DRM device.
   const base::FilePath device_path_;
@@ -192,6 +193,8 @@ 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);
 };