Add type inference for assignment to local variables.

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 7123076acfc0d99e0003b4f086255be60fefc81c..b383f6fcbb9b1f6ac8242d2133a30f39788cc18e 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
@@ -258,6 +258,12 @@ class TypeInferenceListener
   void stringLiteralExit(StringLiteral expression, DartType inferredType) =>
       debugExpressionExit("StringLiteral", expression, inferredType);
 
+  bool variableAssignEnter(Expression expression, DartType typeContext) =>
+      debugExpressionEnter("variableAssign", expression, typeContext);
+
+  void variableAssignExit(Expression expression, DartType inferredType) =>
+      debugExpressionExit("variableAssign", expression, inferredType);
+
   void variableDeclarationEnter(VariableDeclaration statement) =>
       debugStatementEnter('variableDeclaration', statement);