Reapply "Access to imports in the VM's runtime mirrors. Extend test coverage of the source mirrors."

tests/lib/mirrors/library_imports_metadata.dart

Index: tests/lib/mirrors/library_imports_metadata.dart
diff --git a/site/try/bugs/isolate_worker_bug.dart b/tests/lib/mirrors/library_imports_metadata.dart
similarity index 54%
copy from site/try/bugs/isolate_worker_bug.dart
copy to tests/lib/mirrors/library_imports_metadata.dart
index 0f46014e70c45438e9d50b7cf97948aa239d7b08..9507269f47568c6d06a92b099330c183aaaa9ef4 100644
--- a/site/try/bugs/isolate_worker_bug.dart
+++ b/tests/lib/mirrors/library_imports_metadata.dart
@@ -2,15 +2,16 @@
 // 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.
 
-// Successful test: output div contains "future!".
+library library_imports_metadata;
 
-import 'dart:async';
+@m1
+import 'dart:mirrors' as mirrors;
 
-const greeting = "Hello, cool people doing nice things!";
+@m2 @m3
+import 'dart:collection';
 
-// Prints a greeting.
-void main() {
-  print(greeting);
+import 'dart:async';
 
-  new Future(() => print("future!"));
-}
+const m1 = const Object();
+const m2 = const Object();
+const m3 = const Object();