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

pkg/compiler/lib/src/dart_backend/loop_rewriter.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.
 
 library loop_rewriter;
 
 import 'tree_ir_nodes.dart';
 
 /// Rewrites [WhileTrue] statements with an [If] body into a [WhileCondition],
 /// in situations where only one of the branches contains a [Continue] to the
@@ skipping 114 matching lines @@
   Statement visitFunctionDeclaration(FunctionDeclaration node) {
     new LoopRewriter().rewrite(node.definition);
     node.next = visitStatement(node.next);
     return node;
   }
 
   void visitFunctionExpression(FunctionExpression node) {
     new LoopRewriter().rewrite(node.definition);
   }
 }