DevTools: Refactor CallStackSidebarPane.Placard and reveal line on frame restart.

Refactor CallStackSidebarPane.Placard to make it simpler.
As a drive-by: reveal line on frame restart.

R=vsevik@chromium.org, pfeldman, vsevik

Review URL: https://codereview.chromium.org/106793002

git-svn-id: svn://svn.chromium.org/blink/trunk@163310 bbb929c8-8fbe-4397-9dbb-9b2b20218538