1. A method for determining one or more performance metrics for a distributed application in which distributed application data is transferred from a first site to a second site over a network, at least a portion of the method being performed by a computing device comprising at least one processor, the method comprising: receiving a request for the distributed application data, the request being transmitted from the second site to the first site over the network, the time of the request being recorded at the second site using machine instructions; in response to the request, transmitting the distributed application data from the first site to the second site over the network; including machine instructions with the distributed application data that define a performance monitoring function; including a monitor cookie with the distributed application data that indicates that the distributed application data is a monitored object, wherein the monitor cookie enables the second site to: detect that the distributed application data is a monitored object; execute, in response to detecting that the distributed application data is a monitored object, the machine instructions to implement the performance monitoring function to determine the one or more performance metrics for the distributed application without requesting any additional distributed application data from any other site, at least one of the one or more performance metrics being determined using the recorded time of the request.