Reapply "Tweak public APIs and use them in patch_sdk, dart2js, and kernel-service.""

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

Index: pkg/front_end/lib/src/fasta/kernel/utils.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/utils.dart b/pkg/front_end/lib/src/fasta/kernel/utils.dart
index df9748ba387553c27d01cb8690ec00f48eefa775..f77b16dd9d11fd3388a66c7f431f6c0c2d40ca24 100644
--- a/pkg/front_end/lib/src/fasta/kernel/utils.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/utils.dart
@@ -8,6 +8,7 @@ import 'dart:io';
 import 'package:front_end/src/scanner/token.dart' show Token;
 import 'package:kernel/ast.dart';
 import 'package:kernel/binary/ast_to_binary.dart';
+import 'package:kernel/binary/limited_ast_to_binary.dart';
 import 'package:kernel/text/ast_to_text.dart';
 
 /// A null-aware alternative to `token.offset`.  If [token] is `null`, returns
@@ -39,3 +40,26 @@ Future<Null> writeProgramToFile(Program program, Uri uri) async {
     await sink.close();
   }
 }
+
+/// Serialize the libraries in [program] that match [filter].
+List<int> serializeProgram(Program program,
+    {bool filter(Library library), bool excludeUriToSource: false}) {
+  ByteSink byteSink = new ByteSink();
+  BinaryPrinter printer = filter == null && !excludeUriToSource
+      ? new BinaryPrinter(byteSink)
+      : new LimitedBinaryPrinter(
+          byteSink, filter ?? (_) => true, excludeUriToSource);
+  printer.writeProgramFile(program);
+  return byteSink.builder.takeBytes();
+}
+
+/// A [Sink] that directly writes data into a byte builder.
+class ByteSink implements Sink<List<int>> {
+  final BytesBuilder builder = new BytesBuilder();
+
+  void add(List<int> data) {
+    builder.add(data);
+  }
+
+  void close() {}
+}