Make it possible to generate dart:dom and dart:html with a single run of dartdomgenerator.py

[jacob314]

Make it possible to generate dart:dom and dart:html with a single run of dartdomgenerator.py
This will make it more convenient to rebuild everything.
Under the covers we will just close the IDL database as html and dom require conflicting mutations to the IDL

[jacob314]

Added Fixed label.