Repair a CPS integrity violation.

pkg/compiler/lib/src/js_backend/codegen/unsugar.dart

 library dart2js.unsugar_cps;
 
 import '../../cps_ir/cps_ir_nodes.dart';
 
 // TODO(karlklose): share the [ParentVisitor].
 import '../../cps_ir/optimizers.dart';
 import '../../constants/expressions.dart';
 import '../../constants/values.dart';
 import '../../elements/elements.dart'
     show ClassElement, FieldElement, FunctionElement, Element;
@@ skipping 93 matching lines @@
 
     assert(stackTraceParameter.hasNoUses);
     node.handler.parameters.removeLast();
   }
 
   processThrow(Throw node) {
     // The subexpression of throw is wrapped in the JavaScript output.
     Parameter value = new Parameter(null);
     insertStaticCall(_glue.getWrapExceptionHelper(), [node.value.definition],
         value, node);
+    node.value.unlink();
     node.value = new Reference<Primitive>(value);
   }
 
   processInvokeMethod(InvokeMethod node) {
     Selector selector = node.selector;
     // TODO(karlklose):  should we rewrite all selectors?
     if (!_glue.isInterceptedSelector(selector)) return;
 
     Primitive receiver = node.receiver.definition;
     Set<ClassElement> interceptedClasses =
@@ skipping 32 matching lines @@
         new LetPrim(i,
             new Branch(new IsTrue(i),
                 node.trueContinuation.definition,
                 node.falseContinuation.definition)));
     condition.value.unlink();
     node.trueContinuation.unlink();
     node.falseContinuation.unlink();
     parent.body = newNode;
   }
 }