Adds a comment requesting an method type parameter to be kept,
even though it looks redundant, to satisfy OpenJDK.

Review at http://gwt-code-reviews.appspot.com/1730805

Review by: rdayal@google.com

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@11047 8db76d5a-ed1c-0410-87a9-c151d255dfc7