Support enums in dart2dart.

pkg/compiler/lib/src/dart_backend/backend.dart

Index: pkg/compiler/lib/src/dart_backend/backend.dart
diff --git a/pkg/compiler/lib/src/dart_backend/backend.dart b/pkg/compiler/lib/src/dart_backend/backend.dart
index 18cfaae05209a5b10d7485ea851700be700fac60..90baf1b2d30221dea10da42994cd2f62098c638f 100644
--- a/pkg/compiler/lib/src/dart_backend/backend.dart
+++ b/pkg/compiler/lib/src/dart_backend/backend.dart
@@ -233,7 +233,7 @@ class DartBackend extends Backend {
         computeElementAst: computeElementAst,
         shouldOutput: shouldOutput,
         isSafeToRemoveTypeDeclarations: isSafeToRemoveTypeDeclarations,
-        sortElements: sortElements,
+        sortElements: Elements.sortedByPosition,
         mirrorRenamer: mirrorRenamer,
         mainFunction: compiler.mainFunction,
         outputUri: compiler.outputUri);
@@ -468,9 +468,6 @@ compareElements(e0, e1) {
   return compareBy((e) => e.position.charOffset)(e0, e1);
 }
 
-List<Element> sortElements(Iterable<Element> elements) =>
-    sorted(elements, compareElements);
-
 /// [ConstantCompilerTask] for compilation of constants for the Dart backend.
 ///
 /// Since this task needs no distinction between frontend and backend constants