1. A computer-implemented method performed by data processing apparatus, the method comprising: instantiating a native application instance that generates environment instances for display on a user device within the native application instance; in response to the instantiation of the native application instance: determining a memory footprint of the native application instance, the memory footprint specifying an amount of the data processing apparatus memory the native application instance is using at a particular time that the memory footprint is determined; and iteratively monitoring the memory footprint of a native application, the iteratively monitoring comprising, for each iteration: determining a subsequent memory footprint of the native application instance at a time subsequent to a time that a prior memory footprint was determined; determining whether the amount of the data processing apparatus memory specified by the subsequent memory footprint of the native application instance determined at the time subsequent to the time that the prior memory footprint was determined is greater than the amount of the data processing apparatus memory specified by the prior memory footprint; and in response to determining that the subsequent memory footprint of the native application instance determined at the time subsequent to the time that the prior memory footprint was determined is not greater than the prior memory footprint, generating a memory footprint load signal that is a constituent indication that the native application instance is sufficiently instantiated to be subject to a crawling operation.