Move parser helper classes to own files and clean them up.

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

Index: pkg/front_end/lib/src/fasta/builder/formal_parameter_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/builder/formal_parameter_builder.dart b/pkg/front_end/lib/src/fasta/builder/formal_parameter_builder.dart
index ef3f2bf61d31fe8f3951dfd25046f4205889d45e..5be8cd376298acacd4e7eed6c2afb863af377ecf 100644
--- a/pkg/front_end/lib/src/fasta/builder/formal_parameter_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/formal_parameter_builder.dart
@@ -4,7 +4,13 @@
 
 library fasta.formal_parameter_builder;
 
-import '../parser/parser.dart' show FormalParameterType;
+import '../parser.dart' show FormalParameterKind;
+
+import '../parser/formal_parameter_kind.dart'
+    show
+        isMandatoryFormalParameterKind,
+        isOptionalNamedFormalParameterKind,
+        isOptionalPositionalFormalParameterKind;
 
 import 'builder.dart'
     show LibraryBuilder, MetadataBuilder, ModifierBuilder, TypeBuilder;
@@ -25,7 +31,7 @@ abstract class FormalParameterBuilder<T extends TypeBuilder>
   /// True if this parameter is on the form `this.name`.
   final bool hasThis;
 
-  FormalParameterType kind = FormalParameterType.REQUIRED;
+  FormalParameterKind kind = FormalParameterKind.mandatory;
 
   FormalParameterBuilder(this.metadata, this.modifiers, this.type, this.name,
       this.hasThis, LibraryBuilder compilationUnit, this.charOffset)
@@ -33,11 +39,14 @@ abstract class FormalParameterBuilder<T extends TypeBuilder>
 
   String get debugName => "FormalParameterBuilder";
 
-  bool get isRequired => kind.isRequired;
+  bool get isRequired => isMandatoryFormalParameterKind(kind);
 
-  bool get isPositional => kind.isPositional || kind.isRequired;
+  bool get isPositional {
+    return isOptionalPositionalFormalParameterKind(kind) ||
+        isMandatoryFormalParameterKind(kind);
+  }
 
-  bool get isNamed => kind.isNamed;
+  bool get isNamed => isOptionalNamedFormalParameterKind(kind);
 
   bool get isOptional => !isRequired;