Don't return values that aren't used.

pkg/front_end/lib/src/fasta/source/source_library_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.source_library_builder;
 
 import 'package:kernel/ast.dart' show
     AsyncMarker,
     ProcedureKind;
 
 import '../combinator.dart' show
     Combinator;
 
 import '../errors.dart' show
     inputError,
     internalError;
 
 import '../import.dart' show
     Import;
 
 import 'source_loader.dart' show
     SourceLoader;
 
 import '../builder/scope.dart' show
     Scope;
 
 import '../builder/builder.dart' show
     Builder,
-    ClassBuilder,
     ConstructorReferenceBuilder,
-    EnumBuilder,
-    FieldBuilder,
     FormalParameterBuilder,
-    FunctionTypeAliasBuilder,
     LibraryBuilder,
     MemberBuilder,
     MetadataBuilder,
-    NamedMixinApplicationBuilder,
     PrefixBuilder,
-    ProcedureBuilder,
     TypeBuilder,
     TypeDeclarationBuilder,
     TypeVariableBuilder,
     Unhandled;
 
 abstract class SourceLibraryBuilder<T extends TypeBuilder, R>
     extends LibraryBuilder<T, R> {
   final SourceLoader loader;
 
   final DeclarationBuilder<T> libraryDeclaration =
@@ skipping 103 matching lines @@
       resolvedUri = uri.resolve(path);
       newFileUri = fileUri.resolve(path);
     }
     parts.add(loader.read(resolvedUri, newFileUri));
   }
 
   void addPartOf(List<MetadataBuilder> metadata, String name) {
     partOf = name;
   }
 
-  ClassBuilder addClass(List<MetadataBuilder> metadata,
+  void addClass(List<MetadataBuilder> metadata,
       int modifiers, String name,
       List<TypeVariableBuilder> typeVariables, T supertype,
       List<T> interfaces, int charOffset);
 
-  NamedMixinApplicationBuilder addNamedMixinApplication(
+  void addNamedMixinApplication(
       List<MetadataBuilder> metadata, String name,
       List<TypeVariableBuilder> typeVariables, int modifiers,
       T mixinApplication, List<T> interfaces, int charOffset);
 
-  FieldBuilder addField(List<MetadataBuilder> metadata,
+  void addField(List<MetadataBuilder> metadata,
       int modifiers, T type, String name, int charOffset);
 
   void addFields(List<MetadataBuilder> metadata, int modifiers,
       T type, List<String> names) {
     for (String name in names) {
       // TODO(ahe): Get charOffset of name.
       addField(metadata, modifiers, type, name, -1);
     }
   }
 
-  ProcedureBuilder addProcedure(List<MetadataBuilder> metadata,
+  void addProcedure(List<MetadataBuilder> metadata,
       int modifiers, T returnType, String name,
       List<TypeVariableBuilder> typeVariables,
       List<FormalParameterBuilder> formals, AsyncMarker asyncModifier,
       ProcedureKind kind, int charOffset);
 
-  EnumBuilder addEnum(List<MetadataBuilder> metadata, String name,
+  void addEnum(List<MetadataBuilder> metadata, String name,
       List<String> constants, int charOffset);
 
-  FunctionTypeAliasBuilder addFunctionTypeAlias(List<MetadataBuilder> metadata,
+  void addFunctionTypeAlias(List<MetadataBuilder> metadata,
       T returnType, String name,
       List<TypeVariableBuilder> typeVariables,
       List<FormalParameterBuilder> formals, int charOffset);
 
   void addFactoryMethod(List<MetadataBuilder> metadata,
       ConstructorReferenceBuilder name, List<FormalParameterBuilder> formals,
       AsyncMarker asyncModifier, ConstructorReferenceBuilder redirectionTarget,
       int charOffset);
 
   FormalParameterBuilder addFormalParameter(
@@ skipping 213 matching lines @@
           // parent declaration.
           parent.addType(type);
         } else {
           type.bind(builder);
         }
       }
     }
     types.clear();
   }
 }