Avoid crashing on function syntax.

pkg/front_end/lib/src/fasta/builder/function_type_builder.dart

Index: pkg/front_end/lib/src/fasta/builder/function_type_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/builder/function_type_builder.dart b/pkg/front_end/lib/src/fasta/builder/function_type_builder.dart
new file mode 100644
index 0000000000000000000000000000000000000000..4b66b4c515c79d3f695297f6da6d050a70cc37ac
--- /dev/null
+++ b/pkg/front_end/lib/src/fasta/builder/function_type_builder.dart
@@ -0,0 +1,43 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library fasta.function_type_builder;
+
+import 'builder.dart' show LibraryBuilder, TypeBuilder, TypeDeclarationBuilder;
+
+import 'scope.dart' show Scope;
+
+abstract class FunctionTypeBuilder extends TypeBuilder {
+  final TypeBuilder returnType;
+  final List typeVariables;
+  final List formals;
+
+  FunctionTypeBuilder(int charOffset, Uri fileUri, this.returnType,
+      this.typeVariables, this.formals)
+      : super(charOffset, fileUri);
+
+  @override
+  void resolveIn(Scope scope) {}
+
+  @override
+  void bind(TypeDeclarationBuilder builder) {}
+
+  @override
+  String get name => null;
+
+  @override
+  String get debugName => "Function";
+
+  @override
+  StringBuffer printOn(StringBuffer buffer) {
+    buffer.write(typeVariables);
+    buffer.write(formals);
+    buffer.write(" -> ");
+    buffer.write(returnType);
+    return buffer;
+  }
+
+  @override
+  build(LibraryBuilder library) {}
+}