Add renames in output when using the mirror helper library.

sdk/lib/_internal/compiler/implementation/mirrors_used.dart

Index: sdk/lib/_internal/compiler/implementation/mirrors_used.dart
diff --git a/sdk/lib/_internal/compiler/implementation/mirrors_used.dart b/sdk/lib/_internal/compiler/implementation/mirrors_used.dart
index 9c8df9cab5fbe0355c21246f47bedc7b714f2344..144f3950d2abbe5d4f3dff27f6c412c95e5639a5 100644
--- a/sdk/lib/_internal/compiler/implementation/mirrors_used.dart
+++ b/sdk/lib/_internal/compiler/implementation/mirrors_used.dart
@@ -120,8 +120,11 @@ class MirrorUsageAnalyzerTask extends CompilerTask {
   /// the resolver to suppress hints about using new Symbol or
   /// MirrorSystem.getName.
   bool hasMirrorUsage(Element element) {
-    return librariesWithUsage != null
-        && librariesWithUsage.contains(element.getLibrary());
+    LibraryElement library = element.getLibrary();
+    // Internal libraries always have implicit mirror usage.
+    return library.isInternalLibrary
+        || (librariesWithUsage != null
+            && librariesWithUsage.contains(library));
   }
 
   /// Call-back from the resolver to analyze MirorsUsed annotations. The result