Use symbol literals in the mirror tests. (Except for void, the empty string and setters.)

tests/lib/mirrors/to_string_test.dart

Index: tests/lib/mirrors/to_string_test.dart
diff --git a/tests/lib/mirrors/to_string_test.dart b/tests/lib/mirrors/to_string_test.dart
index ac58b2ab5509ba74f8cb2f65f9448f2aa1c1f40d..e8e4e30ac423db520193859f4eceda1590197afe 100644
--- a/tests/lib/mirrors/to_string_test.dart
+++ b/tests/lib/mirrors/to_string_test.dart
@@ -20,7 +20,7 @@ main() {
   expect("TypeMirror on 'dynamic'", mirrors.dynamicType);
   expect("TypeMirror on 'void'", mirrors.voidType);
   expect("LibraryMirror on 'test.to_string_test'",
-         mirrors.findLibrary(const Symbol('test.to_string_test')).single);
+         mirrors.findLibrary(#test.to_string_test).single);
   expect("InstanceMirror on 1", reflect(1));
   expect("ClassMirror on 'Foo'", reflectClass(Foo));
   expect("VariableMirror on 'field'",