Setup correct scope for initializers and complain about fields initialized more than once.

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

Index: pkg/front_end/lib/src/fasta/kernel/kernel_enum_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/kernel_enum_builder.dart b/pkg/front_end/lib/src/fasta/kernel/kernel_enum_builder.dart
index 1673f8de544cb23b102f3d8be8eb2cf81db1453e..75e03191b7203ac88f7fefea0d9dd06d3256522a 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_enum_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_enum_builder.dart
@@ -28,6 +28,8 @@ import 'package:kernel/ast.dart'
         ThisExpression,
         VariableGet;
 
+import 'package:front_end/src/scanner/token.dart' show Token;
+
 import '../errors.dart' show inputError;
 
 import '../modifier.dart' show constMask, finalMask, staticMask;
@@ -120,7 +122,14 @@ class KernelEnumBuilder extends SourceClassBuilder
     ///       String toString() => { 0: ‘E.id0’, . . ., n-1: ‘E.idn-1’}[index]
     ///     }
     members["index"] = new KernelFieldBuilder(
-        null, intType, "index", finalMask, parent, charOffset, null);
+        null,
+        intType,
+        "index",
+        finalMask,
+        parent,
+        charOffset,
+        // Synthetic token to signal this field is initialized.
+        new Token.eof(charOffset));
     KernelConstructorBuilder constructorBuilder = new KernelConstructorBuilder(
         null,
         constMask,
@@ -138,8 +147,15 @@ class KernelEnumBuilder extends SourceClassBuilder
     constructors[""] = constructorBuilder;
     int index = 0;
     List<MapEntry> toStringEntries = <MapEntry>[];
-    KernelFieldBuilder valuesBuilder = new KernelFieldBuilder(null, listType,
-        "values", constMask | staticMask, parent, charOffset, null);
+    KernelFieldBuilder valuesBuilder = new KernelFieldBuilder(
+        null,
+        listType,
+        "values",
+        constMask | staticMask,
+        parent,
+        charOffset,
+        // Synthetic token to signal this field is initialized.
+        new Token.eof(charOffset));
     members["values"] = valuesBuilder;
     KernelProcedureBuilder toStringBuilder = new KernelProcedureBuilder(
         null,
@@ -162,8 +178,15 @@ class KernelEnumBuilder extends SourceClassBuilder
         inputError(null, null, "Duplicated name: $name");
         continue;
       }
-      KernelFieldBuilder fieldBuilder = new KernelFieldBuilder(null, selfType,
-          name, constMask | staticMask, parent, charOffset, null);
+      KernelFieldBuilder fieldBuilder = new KernelFieldBuilder(
+          null,
+          selfType,
+          name,
+          constMask | staticMask,
+          parent,
+          charOffset,
+          // Synthetic token to signal this field is initialized.
+          new Token.eof(charOffset));
       members[name] = fieldBuilder;
       toStringEntries.add(new MapEntry(
           new IntLiteral(index), new StringLiteral("$className.$name")));