Let NaN flow as double into HBranch

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index 7554fd85bad5a136e387698eb704159008be7bdd..830a9f3fc4776019c1377d206336a45725800bc8 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -1600,13 +1600,17 @@ class HBranch: public HUnaryControlInstruction {
       : HUnaryControlInstruction(value, true_target, false_target),
         expected_input_types_(expected_input_types) {
     ASSERT(true_target != NULL && false_target != NULL);
+    SetFlag(kAllowUndefinedAsNaN);
   }
   explicit HBranch(HValue* value)
-      : HUnaryControlInstruction(value, NULL, NULL) { }
+      : HUnaryControlInstruction(value, NULL, NULL) {
+    SetFlag(kAllowUndefinedAsNaN);
+  }
   HBranch(HValue* value, ToBooleanStub::Types expected_input_types)
       : HUnaryControlInstruction(value, NULL, NULL),
-        expected_input_types_(expected_input_types) { }
-
+        expected_input_types_(expected_input_types) {
+    SetFlag(kAllowUndefinedAsNaN);
+  }
 
   virtual Representation RequiredInputRepresentation(int index) {
     return Representation::None();