add MutationObserver polyfill to loader

Add msMatchesSelector to matches impl check

Fix propertyDescriptor for _currentScript

Polyfill document.baseURI for IE

Remove writable, IE doesn't like it

Only need to define baseURI on real document, don't need to keep the prop descriptor around

Add heuristic to fake load event for IE

Spec says that "load" must always be fired on style element, but IE fails to do so if its resources are either fully
text, or the @imports have already been processed asynchornously.

http://www.whatwg.org/specs/web-apps/current-work/multipage/semantics.html#the-style-element

add MutationObserver and WeakMap to karma serve list

Don't try to access CSSRules length if it doesn't exist