Video player: Reset the focus on entering fullscree mode.

ui/file_manager/video_player/js/media_controls.js

Index: ui/file_manager/video_player/js/media_controls.js
diff --git a/ui/file_manager/video_player/js/media_controls.js b/ui/file_manager/video_player/js/media_controls.js
index b718b12718298eebfed5a02ca5cf23e278d36e3a..a2b44eb160d9e17ab3ce523e4c8e10ae94bce0ca 100644
--- a/ui/file_manager/video_player/js/media_controls.js
+++ b/ui/file_manager/video_player/js/media_controls.js
@@ -1093,5 +1093,10 @@ VideoControls.prototype.onFullScreenChanged = function(fullscreen) {
     this.fullscreenButton_.setAttribute('aria-label',
         fullscreen ? str('VIDEO_PLAYER_EXIT_FULL_SCREEN_BUTTON_LABEL')
                    : str('VIDEO_PLAYER_FULL_SCREEN_BUTTON_LABEL'));;
+    // If the fullscreen button has focus on entering fullscreen mode, reset the
+    // focus to make the spacebar toggle play/pause state. This is the
+    // consistent behavior with Youtube Web UI.
+    if (fullscreen)
+      this.fullscreenButton_.blur();
   }
 };