GroupLayerImplTest isn't GWT-compatible

[GoogleCodeExporter]

GroupLayerImplTest isn't GWT compatible so during the GWT compile, some errors 
are emitted:
[ERROR] Line 48: The method shuffle(List<GroupLayerImplTest.TestLayer>) is 
undefined for the type Collections
[ERROR] Line 84: No source code is available for type org.junit.Assert; did you 
forget to inherit a required module?

These can be ignored because the code is never run, but it would be nice to 
either exclude these tests from the GWT code (using <public 
path="...something..."><exclude name="...path...GroupLayerImplTest"/></public>) 
or making the tests GWT compileable.

Original issue reported on code.google.com by pdr@google.com on 18 Jul 2011 at 5:28