Internet Explorer 8 does not support Object.keys.
@Fomafix: Which software project is this about? ULS? MediaWiki core? Adding one is welcome.
MediaWiki core has the es5-shim module, which provides this method (among others). ULS should presumably just add a dependency on it.
es5-ship in core is the right position.
But es5-ship currently does not create Object.keys. This has to be implemented.
Then ULS can depend on es5-ship.
It most definitely does create Object.keys, the code is in /resources/lib/es5-shim/es5-shim.js starting on line 752 onward.
I read the wrong file. es5-shim already creates Object.keys.