Fixing expression extractor & test

Noticed during investigation of https://github.com/angular/angular.dart/pull/747 that this test was not failing when it should have been, there were two issues-
- The packages were not being specified for the test, so the expression extractor was skipping all Angular code.
- The source crawler was not including exported libraries which causes it to incorrectly skip chunks of Angular code.

End result is that the expression list being extracted was a fraction of what it should have been.