Add trace event to SkPicture analysis.

Add trace event to SkPicture analysis.

RE: https://codereview.chromium.org/1319723002/

This should mark out the time spent to support hasText(),
willPlayBackBitmaps(), and numSlowPaths() in about:tracing.

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/e01008fdbccf64eb17f9efe243afdf7aa3f5bd1d

[mtklein_C, 2015-08-27 13:47:24]

mtklein@chromium.org changed reviewers:
+ vmpstr@chromium.org

[mtklein_C, 2015-08-27 13:47:24]

Why wonder how slow it is when we can measure?  :)

[mtklein_C, 2015-08-27 13:47:57]

The CQ bit was checked by mtklein@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-08-27 13:48:10]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1317103002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1317103002/1

[commit-bot: I haz the power, 2015-08-27 13:53:10]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-08-27 13:53:11]

Dry run: This issue passed the CQ dry run.

[vmpstr, 2015-08-27 17:29:30]

lgtm, thanks!

[mtklein, 2015-08-27 17:38:21]

mtklein@google.com changed reviewers:
+ mtklein@google.com

[mtklein, 2015-08-27 17:38:21]

The CQ bit was checked by mtklein@google.com

[mtklein, 2015-08-27 17:38:22]

lgtm

[commit-bot: I haz the power, 2015-08-27 17:38:31]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1317103002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1317103002/1

[commit-bot: I haz the power, 2015-08-27 17:39:09]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/e01008fdbccf64eb17f9efe243afdf7aa3f5bd1d