Make .enclosingClass always return the declaration

pkg/compiler/lib/src/inferrer/inferrer_engine.dart

Index: pkg/compiler/lib/src/inferrer/inferrer_engine.dart
diff --git a/pkg/compiler/lib/src/inferrer/inferrer_engine.dart b/pkg/compiler/lib/src/inferrer/inferrer_engine.dart
index 049a86a798ea10a815a36fea9f6dc6b306301c2b..4623b5c1b5ab3ed65c15bda27b8075aa3c670681 100644
--- a/pkg/compiler/lib/src/inferrer/inferrer_engine.dart
+++ b/pkg/compiler/lib/src/inferrer/inferrer_engine.dart
@@ -834,7 +834,7 @@ class InferrerEngine {
     // If this class has a 'call' method then we have essentially created a
     // closure here. Register it as such so that it is traced.
     if (selector != null && selector.isCall && callee.isConstructor) {
-      ClassElement cls = callee.enclosingClass.declaration;
+      ClassElement cls = callee.enclosingClass;
       if (cls.callType != null) {
         types.allocatedClosures.add(info);
       }