src/vs/workbench/api/common/extHostLanguageFeatures.ts/ExtHostLanguageFeatures/registerDocumentSymbolProvider
class ExtHostLanguageFeatures:	registerDocumentSymbolProvider(extension: IExtensionDescription, selector: vscode.DocumentSelector, provider: vscode.DocumentSymbolProvider, metadata?: vscode.DocumentSymbolProviderMetadata): vscode.Disposable {
		const handle = this._addNewAdapter(new DocumentSymbolAdapter(this._documents, provider), extension);
		const displayName = (metadata && metadata.label) || ExtHostLanguageFeatures._extLabel(extension);
		this._proxy.$registerDocumentSymbolProvider(handle, this._transformDocumentSelector(selector), displayName);
		return this._createDisposable(handle);
	}