estimated_load_progress

An estimate of the percent completion for the current loading operation.

This value will range from 0.0 to 1.0 and, once a load completes, will remain at 1.0 until a new load starts, at which point it will be reset to 0.0. The value is an estimate based on the total number of bytes expected to be received for a document, including all its possible subresources and child documents.