http2/h2demo: show load times on gophertimes demo page
http2/h2demo: show load times on gophertimes demo page

Change-Id: I3d3905adab74a83c9d7d72c829f6686b514f3aaf
Reviewed-on: https://go-review.googlesource.com/15060
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

albertjin/golang-net,gomini/net,cmars/tools,cesanta/goxnet,DramaFever/golang.org-x-net,gomini/net,albertjin/golang-net,cmars/tools,DramaFever/golang.org-x-net,golang/net,cesanta/goxnet,cmars/tools,cmars/tools