Internalize strings in-place

src/objects-debug.cc

Index: src/objects-debug.cc
diff --git a/src/objects-debug.cc b/src/objects-debug.cc
index 51969c5697204230eb06decd9afe8a9b559bcccc..e2eb9e6dc440b21bfde2ed1aa12241861d5d50a5 100644
--- a/src/objects-debug.cc
+++ b/src/objects-debug.cc
@@ -563,9 +563,10 @@ void ConsString::ConsStringVerify() {
   CHECK(this->length() >= ConsString::kMinLength);
   CHECK(this->length() == this->first()->length() + this->second()->length());
   if (this->IsFlat()) {
-    // A flat cons can only be created by String::SlowTryFlatten.
-    // Afterwards, the first part may be externalized.
-    CHECK(this->first()->IsSeqString() || this->first()->IsExternalString());
+    // A flat cons can only be created by String::SlowFlatten.
+    // Afterwards, the first part may be externalized or internalized.
+    CHECK(this->first()->IsSeqString() || this->first()->IsExternalString() ||
+          this->first()->IsThinString());
   }
 }