trace: initialize templates lazily

Parsing the templates can take a significant amount of
time(30-35ms) so it should not be done on the init phase.

Change-Id: I8f258b8028510e698a97b55faeac0d28a61b7b22
Reviewed-on: https://go-review.googlesource.com/21654
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
4 files changed