Make elements/names.dart its own library

pkg/compiler/lib/src/kernel/kernel_visitor.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.md file.
 
 import 'package:kernel/ast.dart' as ir;
 import 'package:kernel/frontend/accessors.dart'
     show
         Accessor,
         IndexAccessor,
         NullAwarePropertyAccessor,
@@ skipping 32 matching lines @@
         FunctionElement,
         FunctionSignature,
         GetterElement,
         InitializingFormalElement,
         JumpTarget,
         LibraryElement,
         LocalElement,
         LocalFunctionElement,
         LocalVariableElement,
         MethodElement,
-        Name,
         ParameterElement,
         PrefixElement,
         TypeVariableElement;
+import '../elements/names.dart' show Name;
 import '../elements/operators.dart'
     show AssignmentOperator, BinaryOperator, IncDecOperator, UnaryOperator;
 import '../elements/resolution_types.dart'
     show ResolutionDartType, ResolutionInterfaceType;
 import '../resolution/semantic_visitor.dart'
     show
         BaseImplementationOfCompoundsMixin,
         BaseImplementationOfLocalsMixin,
         BaseImplementationOfSetIfNullsMixin,
         BaseImplementationOfStaticsMixin,
@@ skipping 2899 matching lines @@
       : this(null, true, node, initializers);
 
   accept(ir.Visitor v) => throw "unsupported";
 
   visitChildren(ir.Visitor v) => throw "unsupported";
 
   String toString() {
     return "IrFunction($kind, $isConstructor, $node, $initializers)";
   }
 }