Internalize strings in-place

src/compiler/access-builder.h

Index: src/compiler/access-builder.h
diff --git a/src/compiler/access-builder.h b/src/compiler/access-builder.h
index f76aedf5a993c85d2cda2cd0645c0988033ca43a..1f56a7fd115f5877b10dc9fd33b8efffb18609b8 100644
--- a/src/compiler/access-builder.h
+++ b/src/compiler/access-builder.h
@@ -172,6 +172,9 @@ class V8_EXPORT_PRIVATE AccessBuilder final
   // Provides access to ConsString::second() field.
   static FieldAccess ForConsStringSecond();
 
+  // Provides access to ThinString::actual() field.
+  static FieldAccess ForThinStringActual();
+
   // Provides access to SlicedString::offset() field.
   static FieldAccess ForSlicedStringOffset();