Rewrite for-in loop as indexing loop for JavaScript indexable arrays

pkg/compiler/lib/src/compiler.dart

Index: pkg/compiler/lib/src/compiler.dart
diff --git a/pkg/compiler/lib/src/compiler.dart b/pkg/compiler/lib/src/compiler.dart
index 4811a94ebb811f4b82fa1fec8c4b8265269c8d31..342f35aa5aa0cd8c41b259611847bb84cefca888 100644
--- a/pkg/compiler/lib/src/compiler.dart
+++ b/pkg/compiler/lib/src/compiler.dart
@@ -564,6 +564,10 @@ class ResolutionCallbacks {
   /// Register an is check to the backend.
   void onIsCheck(DartType type, Registry registry) {}
 
+  /// Called during resolution to notify to the backend that the
+  /// program has a for-in loop.
+  void onSyncForIn(Registry registry) {}
+
   /// Register an as check to the backend.
   void onAsCheck(DartType type, Registry registry) {}