[print] Add external string prefix to string print

Change-Id: I86d8b2046a0809287be31172ec261e4679da66f2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2358731
Commit-Queue: Marja Hölttä <marja@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69416}

src/objects/string.cc

@@ -308,6 +308,8 @@ const char* String::PrefixForDebugPrint() const {
       return "uc\"";
     } else if (shape.IsThin()) {
       return "u>\"";
+    } else if (shape.IsExternal()) {
+      return "ue\"";
     } else {
       return "u\"";
     }
@@ -319,6 +321,8 @@ const char* String::PrefixForDebugPrint() const {
       return "c\"";
     } else if (shape.IsThin()) {
       return ">\"";
+    } else if (shape.IsExternal()) {
+      return "e\"";
     } else {
       return "\"";
     }