Keep in mind that this flag has some issues.
1) The flag is page-level based, but doesn't consider hybrid modes. In other words, this flag is true if the main resource is SPDY based, even if the subresources are not. Likewise, if the main page is loaded via HTTP, but all the subresources are loaded via SPDY, the flag will return false.
2) Chrome is losing track of this flag on page fragments. e.g.
http://www.foo.com/#asdf - the hashtag reload drops the wasFetchedViaSpdy flag. this is a bug.
Mike