pkg/compiler: fix imports

pkg/compiler/lib/src/tree_ir/optimization/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 tree_ir.optimization.loop_rewriter;
 
+import '../tree_ir_nodes.dart';
 import 'optimization.dart' show Pass;
-import '../tree_ir_nodes.dart';
 
 /// Rewrites [WhileTrue] statements into [For] statements.
 ///
 /// Before this phase, loops usually contain a lot of "exit code", that is,
 /// code that happens at a point where a [Continue] can no longer be reached,
 /// and is therefore not really part of the loop.
 /// Exit code is moved down after the loop using the following rewrites rules:
 ///
 /// EXTRACT LABELED STATEMENT:
 ///
@@ skipping 167 matching lines @@
         } else {
           return next;
         }
       }
     }
     // The expression statements could not be pulled into a loop update.
     node.next = next;
     return statements.first;
   }
 }