dart2js: Use an abstract Name class for names in the generated JavaScript ast.

tests/compiler/dart2js/interceptor_test.dart

Index: tests/compiler/dart2js/interceptor_test.dart
diff --git a/tests/compiler/dart2js/interceptor_test.dart b/tests/compiler/dart2js/interceptor_test.dart
index 619d01896028ebcff7141ca520fccfa3794e15ea..c9bd14c39242fc72b57e6be9b44e9b9a294a2ab0 100644
--- a/tests/compiler/dart2js/interceptor_test.dart
+++ b/tests/compiler/dart2js/interceptor_test.dart
@@ -31,7 +31,7 @@ main() {
     // https://code.google.com/p/dart/issues/detail?id=8106.
     compile(TEST_ONE, entry: 'foo', check: (String generated) {
       Expect.isTrue(
-          generated.contains(new RegExp(r'[$A-Z]+\.toString\$0\(a\)')));
+          generated.contains(new RegExp(r'[$A-Z]+\.toString\$0\$\(a\)')));
       Expect.isTrue(generated.contains('myVariableName'));
     }),
     // Check that an intercepted getter that does not need to be