Add type inference logic for "for-in" loops.

pkg/front_end/lib/src/fasta/type_inference/type_inference_listener.dart

Index: pkg/front_end/lib/src/fasta/type_inference/type_inference_listener.dart
diff --git a/pkg/front_end/lib/src/fasta/type_inference/type_inference_listener.dart b/pkg/front_end/lib/src/fasta/type_inference/type_inference_listener.dart
index ace2f8f3f70b1a1415dffca1c8fadc9773418c8a..e8031a3e36eb3130788b63dc83cfb4a34e46969d 100644
--- a/pkg/front_end/lib/src/fasta/type_inference/type_inference_listener.dart
+++ b/pkg/front_end/lib/src/fasta/type_inference/type_inference_listener.dart
@@ -130,6 +130,12 @@ class TypeInferenceListener
   void expressionStatementExit(ExpressionStatement statement) =>
       debugStatementExit('expressionStatement', statement);
 
+  void forInStatementEnter(ForInStatement statement) =>
+      debugStatementEnter('forInStatement', statement);
+
+  void forInStatementExit(ForInStatement statement) =>
+      debugStatementExit('forInStatement', statement);
+
   void functionDeclarationEnter(FunctionDeclaration statement) =>
       debugStatementEnter('functionDeclaration', statement);