[tracing] Mechanical rename of LevelOfDetail enum to enum class.

[tracing] Mechanical rename of LevelOfDetail enum to enum class.

This CL changes the LevelOfDetail enum to enum class to make it easier
to read the code.

TBR=jochen@chromium.org
BUG=499731
Committed: https://crrev.com/297cae0bc0f633a600bc36c09097540a2c03d7f9
Cr-Commit-Position: refs/heads/master@{#342404}

[ssid, 2015-08-07 09:27:01]

ssid@chromium.org changed reviewers:
+ skyostil@chromium.org

[ssid, 2015-08-07 09:27:02]

PTAL. Just renames. Thanks

[Sami, 2015-08-07 09:41:33]

lgtm.

[ssid, 2015-08-07 09:48:37]

ssid@chromium.org changed reviewers:
+ nduca@chromium.org

[ssid, 2015-08-07 09:48:38]

+nduca CL does only renames. PTAL. Thanks

[nduca, 2015-08-07 15:59:34]

lgtm

[ssid, 2015-08-07 16:34:35]

ssid@chromium.org changed reviewers:
+ jochen@chromium.org, reed@google.com

[ssid, 2015-08-07 16:34:36]

Just a rename. I am adding as TBR. Thanks

+reed for skia
+jochen for gin.

[reed1, 2015-08-07 17:11:53]

lgtm

[ssid, 2015-08-07 17:40:11]

The CQ bit was checked by ssid@chromium.org

[commit-bot: I haz the power, 2015-08-07 17:41:11]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1273413002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1273413002/1

[commit-bot: I haz the power, 2015-08-07 19:16:14]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-07 19:17:21]

Patchset 1 (id:??) landed as
https://crrev.com/297cae0bc0f633a600bc36c09097540a2c03d7f9
Cr-Commit-Position: refs/heads/master@{#342404}