The ContextType constants are missing. This makes it hard to feature-detect what context types are supported by the browser.
For the constants to be available like in Chrome and Firefox.
FYI, currently in WebKit, this constant is missing as well. This is tracked in:
https://bugs.webkit.org/show_bug.cgi?id=315666
Version 1.0.7 (146), WebKit 625.1.8
Tahoe (26)
