Fix tools/test.dart dartc/junit_tests callback type error.
Fix tools/test.dart dartc/junit_tests callback type error.

BUG=dart:1025
TEST=tools/test.dart --component=dartc dartc/junit_tests

Review URL: http://codereview.chromium.org//9072006

git-svn-id: c93d8a2297af3b929165606efe145742a534bc71@2917 260f80e4-7a28-3924-810f-c04153c831b5

dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk