DevTools: recognize clicks on Timeline's category label in status bar
DevTools: recognize clicks on Timeline's category label in status bar

We used to only honor checkbox clicks, now we also process label clicks as well.
Drive-by: use createChild() to build DOM.

BUG=
R=loislo@chromium.org

Review URL: https://codereview.chromium.org/23880003

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@157299 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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