Move dart2js from sdk/lib/_internal/compiler to pkg/compiler

pkg/compiler/lib/src/native/js.dart

 // Copyright (c) 2014, 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.
 
 part of native;
 
 class SideEffectsVisitor extends js.BaseVisitor {
   final SideEffects sideEffects;
   SideEffectsVisitor(this.sideEffects);
 
@@ skipping 63 matching lines @@
     node.visitChildren(this);
   }
 
   void visitAccess(js.PropertyAccess node) {
     sideEffects.setDependsOnIndexStore();
     sideEffects.setDependsOnInstancePropertyStore();
     sideEffects.setDependsOnStaticPropertyStore();
     node.visitChildren(this);
   }
 }