1. A computer-implemented method for generating page-level usage data corresponding to interaction with an item of content, the computer-implemented method comprising: as implemented by a computing system comprising one or more computing devices configured with specific executable instructions, transmitting, from the computing system, a content item for output on a client computing device that is distinct from the computing system; receiving, at the computing system, local interaction information from the client computing device, the local interaction information indicating a set of local interaction events implemented locally on the client computing device, during output of the content item, to modify the output of the content item on the client computing device; generating a replay environment, on the computing system, in which to recreate the set of local interaction events; loading the content item within the replay environment generated on the computing system; for individual local interaction events within the set of local interaction events: replaying the individual local interaction event, as previously implemented locally on the client computing device, within the replay environment generated on the computing system; and monitoring a state of the content item loaded within the replay environment generated on the computing system to determine at least a portion of the content item that was output by the client computing device during implementation of the individual local interaction event on the client computing device; based on monitoring the replay environment, generating, at the computing system, information indicative of individual portions of the content item determined to be output by the client computing device during implementation of the set of local interaction events on the client computing device; and storing said information within data storage of the computing system as page-level usage data.