1. A method for automatically instrumenting application code for collecting information during actual use of the application code by field users, the method comprising: inserting one or more logging functions and one or more event handlers into the application code to log events during an execution of the application; automatically inserting code into the application code to assign an identifier for an invocation of an asynchronous call to detour a callback corresponding to the asynchronous call that is made during actual use of the application code in the field to detour code, the detour code being executed to associate the callback with the asynchronous call based upon the identifier; and upon logging the data during execution of the application, matching the asynchronous call to the corresponding callback by: identifying a call site where the asynchronous call was made; assigning a call site identifier to the call site; logging the call site identifier when the callback started executing as an upcall; and associating a beginning of an execution of the callback to the asynchronous call.