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

pkg/compiler/lib/src/js_backend/constant_emitter.dart

 // Copyright (c) 2012, 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 js_backend;
 
 class ConstantEmitter {
   ConstantReferenceEmitter _referenceEmitter;
   ConstantLiteralEmitter _literalEmitter;
 
@@ skipping 373 matching lines @@
       return new jsAst.Call(getHelperProperty(backend.getSetRuntimeTypeInfo()),
                             [value, argumentList]);
     }
     return value;
   }
 
   jsAst.Expression visitDeferred(DeferredConstantValue constant) {
     return constantEmitter.reference(constant.referenced);
   }
 }