1. A computer-implemented method performed by data processing apparatus comprising one or more computers in data communication, the method comprising: for each application page of a native application that generates application pages for display on a user device within the native application, the native application operating independent of a browser application that can operate on the user device: extracting content from the application page, the content including content of a plurality of different content types, the content for each content type being extracted by a corresponding extractor specific to that content type; generating application page data describing content of the application page, the content described by the application page data including text that a user device displays on the application page when the user device displays the application page; and indexing the application page data for the native application in an index that is searchable by a search engine.
8. The computer-implemented method of claim 1 , wherein the content described by the application page data further includes web page link data describing at least one link within the application page that links to a resource referenced by a uniform resource locator that, when selected, instantiates a browser application that renders the resource in a browser environment separate from the native application.