added ErrorEvent WebIDL and errorevent.rs

Removed InitErrorEvent

trying to resolve trace error

moving init in constrictor

removed InitErrorEvent

removed partial from WebIDL, changes in new method and updated test in .ini file

refactoring new_uninitialized

removed unused imports
auto merge of #3822 : RonakNisher/servo/master, r=jdm

Resolved all compilation errors