Sort procedures by source positions.

pkg/front_end/lib/src/fasta/kernel/kernel_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_builder;
 
 export 'kernel_class_builder.dart' show KernelClassBuilder;
 
 export 'kernel_enum_builder.dart' show KernelEnumBuilder;
 
@@ skipping 88 matching lines @@
   charOffset ??= -1;
   if (charOffset == -1) {
     charOffset = member.fileOffset ?? -1;
   }
   if (charOffset == -1) {
     charOffset = cls?.fileOffset ?? -1;
   }
   name = (cls == null ? "" : "${cls.name}::") + name;
   return inputError(uri, charOffset, "Error in $name: $error");
 }
+
+int compareProcedures(Procedure a, Procedure b) {
+  int i = a.fileUri.compareTo(b.fileUri);
+  if (i != 0) return i;
+  return a.fileOffset.compareTo(b.fileOffset);
+}