defined missing constants from previous commit

Author: fath11

src/components/stage-header/stage-header.jsx

@@ -10,7 +10,7 @@ import Button from '../button/button.jsx';
 import ToggleButtons from '../toggle-buttons/toggle-buttons.jsx';
 import Controls from '../../containers/controls.jsx';
 import {getStageDimensions} from '../../lib/screen-utils';
-import {STAGE_DISPLAY_SIZES, STAGE_SIZE_MODES} from '../../lib/layout-constants';
+import {STAGE_DISPLAY_SIZES, STAGE_SIZE_MODES, STAGE_DISPLAY_SCALE_METADATA, FIXED_WIDTH} from '../../lib/layout-constants';
 
 import fullScreenIcon from './icon--fullscreen.svg';
 import unFullScreenIcon from './icon--unfullscreen.svg';