code: function(context, functionName) {
          if (context[functionName].constructor === Function &&
                  context[functionName]._instrumented &&
                  context['_old' + functionName].constructor === Function) {
              context[functionName] = context['_old' + functionName];
          }
      }
docs: Given a context and function name of a function that has been
  instrumented, revert the function to it's original (non-instrumented)
  state.
  
  @param {Object} context of execution (e.g. window)
  @param {String} functionName to de-instrument