Support submillisecond times on FlameChart

With high resolution sampling self/total times can be tenths of millisecond but FlameChart uses 1tick == 1ms scale when displaying time for hovered entry. This patch changes it to show tenths of ms.

BUG=None
R=loislo@chromium.org

Review URL: https://codereview.chromium.org/23924003

git-svn-id: svn://svn.chromium.org/blink/trunk@157362 bbb929c8-8fbe-4397-9dbb-9b2b20218538