JS Debugger: Tooltip for variables should be like Firebug

[salar2k]

Thought it would be nice to have the request reported here too

Bug 1271270
Tooltip for variables should be displayed like the way Firebug displays them.

Notable features:
* Value of variables/object/etc are displayed instantly.
* The tooltips are small and efficient.
* The tooltips moves with mouse while it is on the variable name.
* Tooltips should hide when cursor moves away from the variables.