This adds the ability to add a #x:y anchor to the trace view URL that
causes the viewer to initially select from x ms to y ms.

Change-Id: I4a980d8128ecc85dbe41f224e8ae336707a4eaab
Reviewed-on: https://go-review.googlesource.com/60794
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>