Clean up KernelFormalParameterBuilder

Change-Id: Id0fce5cc75996fd5f88e22a5182b2dc1061d2beb
Reviewed-on: https://dart-review.googlesource.com/73320
Reviewed-by: Jens Johansen <jensj@google.com>
Commit-Queue: Peter von der Ahé <ahe@google.com>

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

@@ -4,7 +4,7 @@
 
 library fasta.kernel_formal_parameter_builder;
 
-import 'kernel_shadow_ast.dart' show VariableDeclarationJudgment;
+import 'package:kernel/ast.dart' show VariableDeclaration;
 
 import '../modifier.dart' show finalMask;
 
@@ -15,12 +15,11 @@ import 'kernel_builder.dart'
         KernelTypeBuilder,
         MetadataBuilder;
 
-import '../source/source_library_builder.dart' show SourceLibraryBuilder;
+import 'kernel_shadow_ast.dart' show VariableDeclarationJudgment;
 
 class KernelFormalParameterBuilder
     extends FormalParameterBuilder<KernelTypeBuilder> {
-  VariableDeclarationJudgment declaration;
-  final int charOffset;
+  VariableDeclaration declaration;
 
   KernelFormalParameterBuilder(
       List<MetadataBuilder> metadata,
@@ -29,13 +28,13 @@ class KernelFormalParameterBuilder
       String name,
       bool hasThis,
       KernelLibraryBuilder compilationUnit,
-      this.charOffset)
+      int charOffset)
       : super(metadata, modifiers, type, name, hasThis, compilationUnit,
             charOffset);
 
-  VariableDeclarationJudgment get target => declaration;
+  VariableDeclaration get target => declaration;
 
-  VariableDeclarationJudgment build(SourceLibraryBuilder library) {
+  VariableDeclaration build(KernelLibraryBuilder library) {
     if (declaration == null) {
       declaration = new VariableDeclarationJudgment(name, 0,
           type: type?.build(library),