Use CompilationUnitBuilder.create factory method.  Remove unneeded
constructor and make single arg constructor private in
ResourceCompilationUnitBuilder and GeneratedCompilationUnitBuilder.

Patch by: stephen.haberman
Review by: zundel
Review at: http://gwt-code-reviews.appspot.com/1465801/


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@10410 8db76d5a-ed1c-0410-87a9-c151d255dfc7