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

pkg/front_end/lib/src/fasta/kernel/body_builder.dart

Index: pkg/front_end/lib/src/fasta/kernel/body_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
index aa73589e5226bcc93c922e6977337093c347159b..66cb325e1abc91ea1177892cb5099d33261f2e2c 100644
--- a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
@@ -510,6 +510,8 @@ class BodyBuilder extends ScopeListener<JumpTarget> implements BuilderHelper {
         VariableDeclaration realParameter = formalBuilders.current.target;
         Expression initializer =
             parameter.initializer ?? new KernelNullLiteral();
+        _typeInferrer.inferParameterInitializer(
+            initializer, realParameter.type);
         realParameter.initializer = initializer..parent = realParameter;
       }
     }