13. A system comprising: one or more non-transitory computer-readable storage media embodying instructions; one or more processors coupled to the media and operable to execute the instructions to: send, to a first computing device from a second computing device, a first request for a view of a user interface of a native application executing on the second computing device, wherein the view includes one or more first user-interface components, and wherein the native application is an application installed locally on the second computing device; receiving, by the second computing device from the first computing device, code implementing a structured document that represents the view, wherein the structured document comprises the one or more first user-interface components as selected by the first computing device and one or more second user-interface components selected by the first computing device based on a user agent type of the second computing device, the second user-interface components associated with a native feature of the second computing device, the native feature comprising a hardware component of the second computing device; receive, by the second computing device, a first user input through the one or more first user-interface components and a second user input through the one or more second user-interface components; send, by the second computing device in response to the first user input, a second request to the first computing device without invoking utilization of the native feature, the second request comprising an application programming interface call to the first computing device; and invoke, by the second computing device in response to the second user input, utilization of the native feature.
13. A system comprising: one or more non-transitory computer-readable storage media embodying instructions; one or more processors coupled to the media and operable to execute the instructions to: send, to a first computing device from a second computing device, a first request for a view of a user interface of a native application executing on the second computing device, wherein the view includes one or more first user-interface components, and wherein the native application is an application installed locally on the second computing device; receiving, by the second computing device from the first computing device, code implementing a structured document that represents the view, wherein the structured document comprises the one or more first user-interface components as selected by the first computing device and one or more second user-interface components selected by the first computing device based on a user agent type of the second computing device, the second user-interface components associated with a native feature of the second computing device, the native feature comprising a hardware component of the second computing device; receive, by the second computing device, a first user input through the one or more first user-interface components and a second user input through the one or more second user-interface components; send, by the second computing device in response to the first user input, a second request to the first computing device without invoking utilization of the native feature, the second request comprising an application programming interface call to the first computing device; and invoke, by the second computing device in response to the second user input, utilization of the native feature. 17. The system of claim 13 , wherein: each second user-interface component is associated with a customized uniform resource locator (URL) referring to the native feature.