Move long-running test to its own test-file.

tests/compiler/dart2js/serialization/test_data.dart

Index: tests/compiler/dart2js/serialization/test_data.dart
diff --git a/tests/compiler/dart2js/serialization/test_data.dart b/tests/compiler/dart2js/serialization/test_data.dart
index 9a24d6570f04dc9476135d3d18fc78c1ef5a7bf8..83cf2da65fd7a70764a7ce9383ba196db942d111 100644
--- a/tests/compiler/dart2js/serialization/test_data.dart
+++ b/tests/compiler/dart2js/serialization/test_data.dart
@@ -5,6 +5,18 @@
 library dart2js.serialization_test_data;
 
 const List<Test> TESTS = const <Test>[
+  // This test is very long-running and put here first to compile it on its own
+  // in compilation0_test.dart
+  const Test('Disable tree shaking through reflection', const {
+    'main.dart': '''
+import 'dart:mirrors';
+
+main() {
+  reflect(null).invoke(#toString, []).reflectee;
+}
+''',
+  }, expectedWarningCount: 1),
+
   const Test('Empty program', const {
     'main.dart': 'main() {}'
   }),
@@ -376,16 +388,6 @@ main() => const String.fromEnvironment("foo");
 ''',
   }),
 
-  const Test('Disable tree shaking through reflection', const {
-    'main.dart': '''
-import 'dart:mirrors';
-
-main() {
-  reflect(null).invoke(#toString, []).reflectee;
-}
-''',
-  }, expectedWarningCount: 1),
-
   const Test('Unused noSuchMethod', const {
     'main.dart': '''
 import 'a.dart';