src/vs/workbench/api/common/extHostQuickOpen.ts/ExtHostQuickOpenImpl/showInput
class ExtHostQuickOpenImpl:		showInput(options?: InputBoxOptions, token: CancellationToken = CancellationToken.None): Promise<string | undefined> {

			// global validate fn used in callback below
			this._validateInput = options ? options.validateInput : undefined;

			return proxy.$input(options, typeof this._validateInput === 'function', token)
				.then(undefined, err => {
					if (isCancellationError(err)) {
						return undefined;
					}

					return Promise.reject(err);
				});
		}