Throw when reflecting on elements not covered by a `MirrorsUsed` annotation.

sdk/lib/_internal/compiler/implementation/js_backend/backend.dart

Index: sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart b/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
index 7a809b704837a6196034428490b1419483c962a2..b01c29b76d51fc6b4c016c6bbd3f26b9ee3486b5 100644
--- a/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
@@ -1534,6 +1534,13 @@ class JavaScriptBackend extends Backend {
     if (metaTargets != null) metaTargetsUsed.addAll(metaTargets);
   }
 
+  /// Returns `true` if [element] can be accessed through reflection, that is,
+  /// is in the set of elements covered by a `MirrorsUsed` annotation.
+  bool isAccessibleByReflection(Element element) {

[ahe, 2013/08/26 20:41:15]

I'm not sure this method is different from isNeededForReflection.

However, it could be a problem that this returns true when
hasInsufficientMirrorsUsed.

The problem is that "isTreeShakingDisabled" means: someone is using reflection
to invoke methods. (Or actually, if isTreeShakingDisabled is false, no methods
are invoked reflectively).

This is important as dart:mirrors may be imported to access
MirrorSystem.getName. But that shouldn't change how methods are generated.

+    if (hasInsufficientMirrorsUsed) return true;
+    return isNeededForReflection(element);
+  }
+
   bool isNeededForReflection(Element element) {
     if (hasInsufficientMirrorsUsed) return isTreeShakingDisabled;
     /// Record the name of [element] in [symbolsUsed]. Return true for