pkg/compiler: fix imports

pkg/compiler/lib/src/tree_ir/optimization/statement_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.statement_rewriter;
 
+import '../../elements/elements.dart';
+import '../../io/source_information.dart';
+import '../../js/placeholder_safety.dart';
+import '../tree_ir_nodes.dart';
 import 'optimization.dart' show Pass;
-import '../tree_ir_nodes.dart';
-import '../../io/source_information.dart';
-import '../../elements/elements.dart';
-import '../../js/placeholder_safety.dart';
 
 /**
  * Translates to direct-style.
  *
  * In addition to the general IR constraints (see [CheckTreeIntegrity]),
  * the input is assumed to satisfy the following criteria:
  *
  * All expressions other than those nested in [Assign] or [ExpressionStatement]
  * must be simple. A [VariableUse] and [This] is a simple expression.
  * The right-hand of an [Assign] may not be an [Assign].
@@ skipping 1360 matching lines @@
 }
 
 /// Decrement the reference count for [e] if it is a variable use.
 void destroyPrimaryExpression(Expression e) {
   if (e is VariableUse) {
     --e.variable.readCount;
   } else {
     assert(e is This);
   }
 }