src/vs/workbench/common/editor/editorGroupModel.ts/EditorGroupModel/doPin
class EditorGroupModel:	private doPin(editor: EditorInput): 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
		this._onDidChangeEditorPinned.fire(editor);
	}