Bug 777196 - Prevent non-chrome processes from accessing the content preferences. r=mak
Bug 882743 - Make TextTrackCue setters throw. r=rillian, r=bz

From 8f5dccf7fd5f5d2a74341ead60586346e4ab3ead Mon Sep 17 00:00:00 2001
Now throwing javascript exceptions from attribute setters for TextTrack-related DOM classes.
As can be seen in http://dev.w3.org/html5/webvtt/#webvtt-api, some of the attributes require validation and throwing.
There is no validation implemented to the align property because there is a bug opened against the spec to change it to an Enum.
When cleared, it should have the IDL changed to remove the throwing.
Validation comments were removed from the properties that didn't have proper validation defined by the spec.