Internalize strings in-place

src/runtime/runtime-internal.cc

Index: src/runtime/runtime-internal.cc
diff --git a/src/runtime/runtime-internal.cc b/src/runtime/runtime-internal.cc
index baeba346a5185761941f27a28ac233e6d00f1b3f..6923427c5ee703bc089125e79325cc621bdee783 100644
--- a/src/runtime/runtime-internal.cc
+++ b/src/runtime/runtime-internal.cc
@@ -290,6 +290,7 @@ RUNTIME_FUNCTION(Runtime_AllocateSeqOneByteString) {
   HandleScope scope(isolate);
   DCHECK_EQ(1, args.length());
   CONVERT_SMI_ARG_CHECKED(length, 0);
+  if (length == 0) return isolate->heap()->empty_string();
   Handle<SeqOneByteString> result;
   ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
       isolate, result, isolate->factory()->NewRawOneByteString(length));
@@ -300,6 +301,7 @@ RUNTIME_FUNCTION(Runtime_AllocateSeqTwoByteString) {
   HandleScope scope(isolate);
   DCHECK_EQ(1, args.length());
   CONVERT_SMI_ARG_CHECKED(length, 0);
+  if (length == 0) return isolate->heap()->empty_string();
   Handle<SeqTwoByteString> result;
   ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
       isolate, result, isolate->factory()->NewRawTwoByteString(length));