Timeline: add layer details view

Timeline: add layer details view

This brings layer details view from Layers panel to Timeline's layer
tree view. Also:

- fixed trace layer import to include compositing reasons from trace;
- show compositing traces as a list of user-friendly (long) strings.

BUG=

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=184010

[caseq, 2014-10-20 14:15:06]

caseq@chromium.org changed reviewers:
+ pfeldman@chromium.org, yurys@chromium.org

[pfeldman, 2014-10-20 14:58:01]

lgtm

[caseq, 2014-10-20 17:18:25]

The CQ bit was checked by caseq@chromium.org

[commit-bot: I haz the power, 2014-10-20 17:19:37]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/670503002/1

[commit-bot: I haz the power, 2014-10-20 20:26:24]

Committed patchset #1 (id:1) as 184010