GWT tests do not restrict permutations properly

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What steps will reproduce the problem?
1. Run a gwt test.

What is the expected output? What do you see instead?
Expected output is something within a few minutes.  Instead, it takes way too 
long, and even a trivial test can timeout due to the large number of default 
permutations that are being frivolously compiled.

The only permutations that should be used for GWT tests, if any, are user-agent 
permutations.  It's just not practical to have any more than that.

My suggestion is to be simple, and make all test modules declare explicitly the 
exact number of permutations in which it should run, by inheriting from 
restrictors that should be littered around a few top-level packages (e.g., 
OnePermutation.gwt.xml and AllPermutations.gwt.xml).  The default should always 
be OnePermutation.

Of course, nothing can enforce anything about the number of permutations that 
are used for a test, because of the brittleness and non-locality of how 
restrictions work with module definitions, but it should be an improvement.

Original issue reported on code.google.com by hearn...@google.com on 22 Feb 2011 at 12:18

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edit: GWT tests are already restricted by user-agent, but all the other 
dimensions (locale, log-level, etc) are not necessarily restricted.

Original comment by hearn...@google.com on 22 Feb 2011 at 12:59