Remember and reuse derived map for external arrays

src/property.cc

Index: src/property.cc
diff --git a/src/property.cc b/src/property.cc
index 96774333e812a9d9676454ef8cf2e2428c42bfeb..c35fb8347409a34732ab05fb8091d58d55e5a7d6 100644
--- a/src/property.cc
+++ b/src/property.cc
@@ -52,6 +52,12 @@ void LookupResult::Print(FILE* out) {
       GetTransitionMap()->Print(out);
       PrintF(out, "\n");
       break;
+    case EXTERNAL_ARRAY_TRANSITION:
+      PrintF(out, " -type = external array transition\n");
+      PrintF(out, " -map:\n");
+      GetTransitionMap()->Print(out);
+      PrintF(out, "\n");
+      break;
     case CONSTANT_FUNCTION:
       PrintF(out, " -type = constant function\n");
       PrintF(out, " -function:\n");