src/vs/workbench/common/editor/editorGroupModel.ts/EditorGroupModel/doPin
class EditorGroupModel:	private doPin(editor: EditorInput, editorIndex: number): void {
		if (this.isPinned(editor)) {
			return; // can only pin a preview editor
		}

		// Convert the preview editor to be a pinned editor
		this.preview = null;

		// Event
		const event: IGroupEditorChangeEvent = {
			kind: GroupModelChangeKind.EDITOR_PIN,
			editor,
			editorIndex
		};
		this._onDidModelChange.fire(event);
	}