Perform type inference on default values of optional/named parameters.

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

Index: pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
diff --git a/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart b/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
index 5e064d168d61c397e9f89fb6ab510b72f0e6a0e0..dc9d033e9584b9717516fb3ef72f8aede2087baa 100644
--- a/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
+++ b/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
@@ -177,6 +177,10 @@ abstract class TypeInferrer {
 
   /// Performs type inference on the given constructor initializer.
   void inferInitializer(Initializer initializer);
+
+  /// Performs type inference on the given function parameter initializer
+  /// expression.
+  void inferParameterInitializer(Expression initializer, DartType declaredType);
 }
 
 /// Derived class containing generic implementations of [TypeInferrer].
@@ -489,6 +493,13 @@ abstract class TypeInferrerImpl extends TypeInferrer {
     return inferredType;
   }
 
+  @override
+  void inferParameterInitializer(
+      Expression initializer, DartType declaredType) {
+    assert(closureContext == null);
+    inferExpression(initializer, declaredType, false);
+  }
+
   /// Modifies a type as appropriate when inferring a closure return type.
   DartType inferReturnType(DartType returnType, bool isExpressionFunction) {
     if (returnType == null) {