src/vs/editor/common/config/editorOptions.ts/EditorTabFocusMode/compute
class EditorTabFocusMode:	public compute(env: IEnvironmentalOptions, options: IComputedEditorOptions, _: boolean): boolean {
		const readOnly = options.get(EditorOption.readOnly);
		return (readOnly ? true : env.tabFocusMode);
	}