Avoid crashing on function syntax.

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

 // Copyright (c) 2016, 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.kernel_library_builder;
 
 import 'package:kernel/ast.dart';
 
 import 'package:kernel/clone.dart' show CloneVisitor;
 
@@ skipping 16 matching lines @@
         ClassBuilder,
         ConstructorReferenceBuilder,
         DynamicTypeBuilder,
         FormalParameterBuilder,
         FunctionTypeAliasBuilder,
         KernelConstructorBuilder,
         KernelEnumBuilder,
         KernelFieldBuilder,
         KernelFormalParameterBuilder,
         KernelFunctionTypeAliasBuilder,
+        KernelFunctionTypeBuilder,
         KernelInvalidTypeBuilder,
         KernelMixinApplicationBuilder,
         KernelNamedMixinApplicationBuilder,
         KernelNamedTypeBuilder,
         KernelProcedureBuilder,
         KernelTypeBuilder,
         KernelTypeVariableBuilder,
         MemberBuilder,
         MetadataBuilder,
         MixedAccessor,
@@ skipping 205 matching lines @@
       List<TypeVariableBuilder> typeVariables,
       List<FormalParameterBuilder> formals,
       int charOffset) {
     FunctionTypeAliasBuilder typedef = new KernelFunctionTypeAliasBuilder(
         metadata, returnType, name, typeVariables, formals, this, charOffset);
     // Nested declaration began in `OutlineBuilder.beginFunctionTypeAlias`.
     endNestedDeclaration().resolveTypes(typeVariables, this);
     addBuilder(name, typedef, charOffset);
   }
 
+  KernelFunctionTypeBuilder addFunctionType(
+      KernelTypeBuilder returnType,
+      List<TypeVariableBuilder> typeVariables,
+      List<FormalParameterBuilder> formals,
+      int charOffset) {
+    return new KernelFunctionTypeBuilder(
+        charOffset, fileUri, returnType, typeVariables, formals);
+  }
+
   KernelFormalParameterBuilder addFormalParameter(
       List<MetadataBuilder> metadata,
       int modifiers,
       KernelTypeBuilder type,
       String name,
       bool hasThis,
       int charOffset) {
     return new KernelFormalParameterBuilder(
         metadata, modifiers, type, name, hasThis, this, charOffset);
   }
@@ skipping 139 matching lines @@
   }
 }
 
 bool isConstructorName(String name, String className) {
   if (name.startsWith(className)) {
     if (name.length == className.length) return true;
     if (name.startsWith(".", className.length)) return true;
   }
   return false;
 }