Add a test that uses the processor libs on Windows

Similar to some of the tests I wrote for Mac and Linux, this lets us use the
processor libs in Windows client unittests. This is useful for ensuring that the
dump generation code produces the expected output in certain circumstances. The
actual test added here isn't very useful, but I have another patch coming right
up that uses this.

[Mark Mentovai]

LGTM

http://breakpad.appspot.com/258001/diff/1/4
File src/client/windows/unittests/exception_handler_test.cc (right):

http://breakpad.appspot.com/258001/diff/1/4#newcode377
Line 377: }
}  // namespace