WebKitPerfMonitor: Tooltips can be cut off at the top

WebKitPerfMonitor: Tooltips can be cut off at the top
https://bugs.webkit.org/show_bug.cgi?id=130960

Reviewed by Andreas Kling.

* public/common.css:
(#title): Removed the gradients, box shadows, and border from the header.
(#title h1): Reduce the font size.
(#title ul): Use line-height to vertically align the navigation bar instead of specifying a padding atop.
* public/index.html:
(.tooltop:before): Added. Identical to .tooltop:after except it's upside down (arrow facing up).
(.tooltip.inverted:before): Show the arrow facing up when .inverted is set.
(.tooltip.inverted:before): Hide the arrow facing down when .inverted is set.
* public/js/helper-classes.js:
(Tooltip.show): Show the tooltip below the point if placing it above the point results in the top of the
tooltip extending above y=0.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@166701 268f45cc-cd09-0410-ab3c-d52691b4dbfc