dart2js cps: Prefer unlabeled continue over labeled break.

pkg/compiler/lib/src/js_backend/codegen/codegen.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 code_generator;
 
 import 'glue.dart';
 
 import '../../closure.dart' show
     ClosureClassElement;
@@ skipping 453 matching lines @@
     }
   }
 
   /// True if [other] is the target of [node] or is a [Break] with the same
   /// target. This means jumping to [other] is equivalent to executing [node].
   bool isEffectiveBreakTarget(tree_ir.Break node, tree_ir.Statement other) {
     return node.target.binding.next == other ||
            other is tree_ir.Break && node.target == other.target;
   }
 
+  /// True if the given break is equivalent to an unlabeled continue.
+  bool isShortContinue(tree_ir.Break node) {
+    tree_ir.Statement next = node.target.binding.next;
+    return next is tree_ir.Continue &&
+           next.target.binding == shortContinue.target;
+  }
+
   @override
   void visitBreak(tree_ir.Break node) {
     if (isEffectiveBreakTarget(node, fallthrough.target)) {
       // Fall through to break target or to equivalent break.
       fallthrough.use();
     } else if (isEffectiveBreakTarget(node, shortBreak.target)) {
       // Unlabeled break to the break target or to an equivalent break.
       shortBreak.use();
       accumulator.add(new js.Break(null));
+    } else if (isShortContinue(node)) {
+      // An unlabeled continue is better than a labeled break.
+      shortContinue.use();
+      accumulator.add(new js.Continue(null));
     } else {
       usedLabels.add(node.target);
       accumulator.add(new js.Break(node.target.name));
     }
   }
 
   @override
   void visitExpressionStatement(tree_ir.ExpressionStatement node) {
     accumulator.add(new js.ExpressionStatement(
         visitExpression(node.expression)));
@@ skipping 537 matching lines @@
   void registerDefaultParameterValues(ExecutableElement element) {
     if (element is! FunctionElement) return;
     FunctionElement function = element;
     if (function.isStatic) return; // Defaults are inlined at call sites.
     function.functionSignature.forEachOptionalParameter((param) {
       ConstantValue constant = glue.getDefaultParameterValue(param);
       registry.registerCompileTimeConstant(constant);
     });
   }
 }