Ensure locations are always provided, but don't store them yet.

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

Index: pkg/front_end/lib/src/fasta/builder/field_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/builder/field_builder.dart b/pkg/front_end/lib/src/fasta/builder/field_builder.dart
index 1625cd151d50c21458bceaefc05c55ac75b52518..1fdd6e69cab6cd0713f0e8d5b8b0d6f78054d151 100644
--- a/pkg/front_end/lib/src/fasta/builder/field_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/field_builder.dart
@@ -5,6 +5,7 @@
 library fasta.field_builder;
 
 import 'builder.dart' show
+    LibraryBuilder,
     MemberBuilder;
 
 abstract class FieldBuilder<T> extends MemberBuilder {
@@ -12,7 +13,9 @@ abstract class FieldBuilder<T> extends MemberBuilder {
 
   final int modifiers;
 
-  FieldBuilder(this.name, this.modifiers);
+  FieldBuilder(this.name, this.modifiers, LibraryBuilder compilationUnit,
+      int charOffset)
+      : super(compilationUnit, charOffset);
 
   void set initializer(T value);