Adjust mirrors/regress_19731_test to avoid static warnings.

tests/lib/mirrors/regress_19731_test.dart

Index: tests/lib/mirrors/regress_19731_test.dart
diff --git a/tests/lib/mirrors/regress_19731_test.dart b/tests/lib/mirrors/regress_19731_test.dart
index 03e7facbc593579deba74a2bb10f2450c6f79cb2..b3680028c1b9cbc18657c88d400be17ee64a62f0 100644
--- a/tests/lib/mirrors/regress_19731_test.dart
+++ b/tests/lib/mirrors/regress_19731_test.dart
@@ -23,11 +23,13 @@ class OneField {
 method() {}
 
 main() {
-  var classFieldNames = reflectType(OneField).declarations.values
+  var classMirror = reflectType(OneField);
+  var classFieldNames = classMirror.declarations.values
     .where((v) => v is VariableMirror).map((v) => v.simpleName).toList();
   Expect.setEquals([#onlyClassField], classFieldNames);
 
-  var libraryFieldNames = reflectType(OneField).owner.declarations.values
+  var libraryMirror = classMirror.owner;
+  var libraryFieldNames = libraryMirror.declarations.values
     .where((v) => v is VariableMirror).map((v) => v.simpleName).toList();
   Expect.setEquals([#metadata], libraryFieldNames);
 }