webkit desktop notification

Implement webkit dekstop notification (with image url and event dispatcher for click, close, display, error to javascript)
currently only implemented for Windows and MAC

the windows version will need some chrome source modification, I've made the pull request here:
https://github.com/rogerwang/chromium.src/pull/12 
sorry about that, I use Xcode and Vstudio, apparently Xcode uses space, Vstudio uses tab