fix crash in VM type checked mode

fix crash in VM type checked mode
Committed: https://code.google.com/p/dart/source/detail?r=6721

[Emily Fortuna, 2012-04-19 01:02:34]

Fixing Issue 2625. My initial fix was wrong, because processQueue can be null
when running VM tests. 

HOWEVER, this fix feels really unsatisfactory... I don't understand how
testCase.configuration['verbose'] could be null.... it is already initialized to
false in line 189 in test_options.dart and then used without testing for null in
later places -- such as line 454 in test_options.dart.

[Siggi Cherem (dart-lang), 2012-04-19 01:10:40]

lgtm