SkPDF: add some TRACE_EVENTs

Change-Id: I5f7e7ad57c1e585254378e3fdee4d33c3582d7c2
Reviewed-on: https://skia-review.googlesource.com/20517
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>
2 files changed