Right now the algorithm doesn't include any iFrames on the page. We can add timing for any iframes that are not blocked by security restrictions:

• Modify the RUMSpeedIndex function to take a window to operate on (default to the top-level window if not specified)
• Enumerate any visible iFrames, record their visible area and run RUMSpeedIndex on the iFrame
• Add the iFrame speed index as a paint time for the area of the iFrame (Speed Index is effectively the average paint time)

This should recursively walk frames regardless of how deep they are nested.