DevTools: REGRESSION: FlameChart doesn't highlight the bar under mouse pointer.

Regressed at r157451.
highlighted index is absolute.
So we should compare entries by value.

BUG=none
R=yurys@chromium.org

Review URL: https://codereview.chromium.org/25261002

git-svn-id: svn://svn.chromium.org/blink/trunk@158538 bbb929c8-8fbe-4397-9dbb-9b2b20218538