Short-circuit embedded cons strings.

src/hydrogen-instructions.cc

Index: src/hydrogen-instructions.cc
diff --git a/src/hydrogen-instructions.cc b/src/hydrogen-instructions.cc
index f4a92a5316d3bca8a58df6fff3e39de8c96486d0..ce077852816372e2dd9158754255a2d5a2f29a7b 100644
--- a/src/hydrogen-instructions.cc
+++ b/src/hydrogen-instructions.cc
@@ -3328,7 +3328,7 @@ HInstruction* HStringAdd::New(
     HConstant* c_right = HConstant::cast(right);
     HConstant* c_left = HConstant::cast(left);
     if (c_left->HasStringValue() && c_right->HasStringValue()) {
-      Factory* factory = Isolate::Current()->factory();
+      Factory* factory = zone->isolate()->factory();
       return new(zone) HConstant(factory->NewConsString(c_left->StringValue(),
                                                         c_right->StringValue()),
                                  Representation::Tagged());