src/vs/editor/browser/widget/codeEditorWidget.ts/EditorContextKeysManager/_updateFromModel
class EditorContextKeysManager:	private _updateFromModel(): void {
		const model = this._editor.getModel();
		this._canUndo.set(Boolean(model && model.canUndo()));
		this._canRedo.set(Boolean(model && model.canRedo()));
	}