dart2js cps: Compile some loops as 'for' loops.

pkg/compiler/lib/src/tree_ir/optimization/variable_merger.dart

 // Copyright (c) 2015, 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.variable_merger;
 
 import 'optimization.dart' show Pass;
 import '../tree_ir_nodes.dart';
 
 /// Merges variables based on liveness and source variable information.
@@ skipping 191 matching lines @@
   }
 
   visitWhileTrue(WhileTrue node) {
     Block join = _jumpTarget[node.label] = newBlock();
     join.predecessors.add(_currentBlock);
     _currentBlock = join;
     visitStatement(node.body); // visitContinue will add predecessors to join.
   }
 
   visitWhileCondition(WhileCondition node) {
-    Block join = _jumpTarget[node.label] = newBlock();
-    join.predecessors.add(_currentBlock);
-    _currentBlock = join;
+    Block entry = _currentBlock;
+    _currentBlock = _jumpTarget[node.label] = newBlock();
+    node.updates.forEach(visitExpression);
+    joinFrom(entry, _currentBlock);
     visitExpression(node.condition);
     Block afterCondition = _currentBlock;
     branchFrom(afterCondition);
     visitStatement(node.body); // visitContinue will add predecessors to join.
     branchFrom(afterCondition);
     visitStatement(node.next);
   }
 
   visitTry(Try node) {
     Block outerCatchBlock = _currentBlock.catchBlock;
@@ skipping 310 matching lines @@
     node.expression = visitExpression(node.expression);
     node.next = visitStatement(node.next);
     if (node.expression is VariableUse) {
       VariableUse use = node.expression;
       --use.variable.readCount;
       return node.next;
     }
     return node;
   }
 }