1. A method of performing speech recognition that is performed by one or more computers of an automated speech recognizer, the method comprising: receiving, by the one or more computers, data that indicates multiple candidate transcriptions for an utterance, wherein the one or more computers are in communication with (i) a first search system that provides a search service of a first domain, and (ii) a second search system that provides a search service for a second domain, the second domain being different from the first domain; for each particular candidate transcription of the candidate transcriptions: receiving, by the one or more computers, data from the first search system that provides the search service for the first domain, the data from the first search system indicating first search results that the search service for the first domain identifies as relevant to the particular candidate transcription; determining, by the one or more computers, a first score based on the first search results that the search service for the first domain identifies as relevant to the particular candidate transcription; receiving, by the one or more computers, data from the second search system that provides the search service for the second domain, the data from the second search system indicating second search results that the search service for the second domain identifies as relevant to the particular candidate transcription; determining, by the one or more computers, a second score based on the second search results that the search service for the second domain identifies as relevant to the particular candidate transcription; providing, by the one or more computers, (i) the first score that is determined based on the first search results and (ii) the second score that is determined based on the second search results as input to a classifier, wherein the classifier has been trained, using scores that represent characteristics of different search results from different domains, to indicate a likelihood that a transcription is correct based on scores for multiple different domains; and receiving, by the one or more computers and from the trained classifier, a classifier output in response to at least the first score and the second score, the classifier output indicating a likelihood that the particular candidate transcription is correct; selecting, by the one or more computers, a transcription for the utterance, from among the multiple candidate transcriptions, based on the classifier outputs; and providing, by the one or more computers, the transcription as output of the automated speech recognizer.