Internalize strings in-place

src/regexp/regexp-macro-assembler.cc

Index: src/regexp/regexp-macro-assembler.cc
diff --git a/src/regexp/regexp-macro-assembler.cc b/src/regexp/regexp-macro-assembler.cc
index 0a7f5c1b9e295727ac672cc008adee0dbfc41ed6..73797e4416b8b198e3c13df50b56587bd6c04fa3 100644
--- a/src/regexp/regexp-macro-assembler.cc
+++ b/src/regexp/regexp-macro-assembler.cc
@@ -133,6 +133,8 @@ const byte* NativeRegExpMacroAssembler::StringCharacterPosition(
   } else if (subject->IsSlicedString()) {
     start_index += SlicedString::cast(subject)->offset();
     subject = SlicedString::cast(subject)->parent();
+  } else if (subject->IsThinString()) {
+    subject = ThinString::cast(subject)->actual();
   }
   DCHECK(start_index >= 0);
   DCHECK(start_index <= subject->length());
@@ -239,6 +241,9 @@ NativeRegExpMacroAssembler::Result NativeRegExpMacroAssembler::Match(
     subject_ptr = slice->parent();
     slice_offset = slice->offset();
   }
+  if (StringShape(subject_ptr).IsThin()) {
+    subject_ptr = ThinString::cast(subject_ptr)->actual();
+  }
   // Ensure that an underlying string has the same representation.
   bool is_one_byte = subject_ptr->IsOneByteRepresentation();
   DCHECK(subject_ptr->IsExternalString() || subject_ptr->IsSeqString());