[Resource Timing] Initial “about blank” for iframe

In latest Resource Timing draft [1], example 3 of section 4.2 says:
“…the user agent may fetch an about:blank resource for the IFRAME. If at a later time the src attribute is changed dynamically via script, the user agent may fetch the new URL resource for the IFRAME. In this case, both the fetch of the about:blank resource, as well as the fetch of the new URL would be included as PerformanceResourceTiming”
I noticed this example doesn’t exist in CR version [2], and was added from June 27, 2012 draft [3], however I didn’t find a discussion about it.

Why the initial “about:blank” item should be included? I can’t imagine it is fetched from networking layer. I think it would make more sense if it is:
“…In this case, the fetch of the new URL should be included as PerformanceResourceTiming”.
You idea? ☺

[1] https://dvcs.w3.org/hg/webperf/raw-file/tip/specs/ResourceTiming/Overview.html

[2] http://www.w3.org/TR/resource-timing/

[3] http://dvcs.w3.org/hg/webperf/raw-file/9f30b23d0d99/specs/ResourceTiming/Overview.html


thanks
Pan