Revert of 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 5caf12a7be3b258a12fe7cdc289a8c6d0c321eef..ee39fdd069c43bd2b35e2ccf27ac6ef21a3a3aed 100644
--- a/src/objects-debug.cc
+++ b/src/objects-debug.cc
@@ -555,8 +555,6 @@
     ConsString::cast(this)->ConsStringVerify();
   } else if (IsSlicedString()) {
     SlicedString::cast(this)->SlicedStringVerify();
-  } else if (IsThinString()) {
-    ThinString::cast(this)->ThinStringVerify();
   }
 }
 
@@ -568,16 +566,12 @@
   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::SlowFlatten.
-    // Afterwards, the first part may be externalized or internalized.
-    CHECK(this->first()->IsSeqString() || this->first()->IsExternalString() ||
-          this->first()->IsThinString());
-  }
-}
-
-void ThinString::ThinStringVerify() {
-  CHECK(this->actual()->IsInternalizedString());
-}
+    // A flat cons can only be created by String::SlowTryFlatten.
+    // Afterwards, the first part may be externalized.
+    CHECK(this->first()->IsSeqString() || this->first()->IsExternalString());
+  }
+}
+
 
 void SlicedString::SlicedStringVerify() {
   CHECK(!this->parent()->IsConsString());