Add trace events for shader generation.

This helps explain why some frames are slow in Flutter.

Change-Id: Ic8b36186f1c8c262950e5ff9e0da3b808cff8d0c
Reviewed-on: https://skia-review.googlesource.com/22087
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
3 files changed