dart2js cps: Do not add identical calls for foreign code conditions.

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

 library dart2js.unsugar_cps;
 
 import '../../cps_ir/cps_ir_nodes.dart';
 
 import '../../cps_ir/optimizers.dart' show ParentVisitor;
 import '../../constants/values.dart';
 import '../../elements/elements.dart';
 import '../../io/source_information.dart';
 import '../../js_backend/codegen/glue.dart';
 import '../../universe/universe.dart' show Selector;
@@ skipping 275 matching lines @@
       // getInterceptor again, so the receiver must be the interceptor (likely
       // `this`), not `null`.
       node.receiver = new Reference<Primitive>(nullPrim);
     }
   }
 
   processBranch(Branch node) {
     // TODO(karlklose): implement the checked mode part of boolean conversion.
     InteriorNode parent = node.parent;
     IsTrue condition = node.condition;
+
+    // Do not rewrite conditions that are foreign code.
+    // It is redundant, and causes infinite recursion (if not optimized)
+    // in the implementation of identical, which itself contains a condition.
+    Primitive value = condition.value.definition;
+    if (value is Parameter && value.parent is Continuation) {
+      Continuation cont = value.parent;
+      if (cont.hasExactlyOneUse && cont.firstRef.parent is ForeignCode) {
+        ForeignCode foreign = cont.firstRef.parent;
+        if (foreign.type.containsOnlyBool(_glue.classWorld)) {
+          return;
+        }
+      }
+    }
+
     Primitive t = trueConstant;
     Primitive i = new ApplyBuiltinOperator(
         BuiltinOperator.Identical,
         <Primitive>[condition.value.definition, t],
         condition.value.definition.sourceInformation);
     LetPrim newNode = new LetPrim(t,
         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;
   }
 
   processInterceptor(Interceptor node) {
     _glue.registerSpecializedGetInterceptor(node.interceptedClasses);
   }
 }