Fix dart2js warnings and add test to ensure it stays clean.

pkg/testing/lib/src/test_dart/status_expression.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-library status_expression;
+library test_dart_copy.status_expression;
 
 /**
  * Parse and evaluate expressions in a .status file for Dart and V8.
  * There are set expressions and Boolean expressions in a .status file.
  * The grammar is:
  *   BooleanExpression := $variableName == value | $variableName != value |
  *                        $variableName | (BooleanExpression) |
  *                        BooleanExpression && BooleanExpression |
  *                        BooleanExpression || BooleanExpression
  *
@@ skipping 289 matching lines @@
             "Expected value in expression, got ${scanner.current}");
       }
       TermConstant right = new TermConstant(scanner.current);
       scanner.advance();
       return new Comparison(left, right, negate);
     } else {
       return new BooleanVariable(left);
     }
   }
 }