Web Inspector: Flame Chart. Provide node context info in a popover when mouse hovers...

Web Inspector: Flame Chart. Provide node context info in a popover when mouse hovers over a flame chart item.
https://bugs.webkit.org/show_bug.cgi?id=111442

Reviewed by Yury Semikhatsky.

FlameChart is a canvas so it is not possible to attach the popover to the items on it.
It would be a bit tricky to support an offset due to complex behaviour of the popover.
The simplest solution is to create a fake anchor element and move it to the right position.

* inspector/front-end/FlameChart.js:
(WebInspector.FlameChart):
(WebInspector.FlameChart.prototype._getPopoverAnchor):
(WebInspector.FlameChart.prototype._showPopover):
(WebInspector.FlameChart.prototype._onMouseMove):
(WebInspector.FlameChart.prototype.findNodeCallback):
(WebInspector.FlameChart.prototype._coordinatesToNode):
(WebInspector.FlameChart.prototype.onResize):
* inspector/front-end/flameChart.css:
(.flame-chart .item-anchor):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@144888 268f45cc-cd09-0410-ab3c-d52691b4dbfc