NullPrincipal::Create() (will null OA) may cause an OriginAttributes bypass.
We change Create() so OriginAttributes is no longer optional, and rename
Create() with no arguments to make it more explicit about what the caller is doing.
MozReview-Commit-ID: 7DQGlgh1tgJ
This patch does the following in addition to a simple move:
* change the type of the pointers from RefPtr to nsCOMPtr
* move it from mozilla::css namespace to mozilla
MozReview-Commit-ID: 72MYq6kWm4s
