Generated code for substring slices in x64 and arm.

src/x64/macro-assembler-x64.h

Index: src/x64/macro-assembler-x64.h
diff --git a/src/x64/macro-assembler-x64.h b/src/x64/macro-assembler-x64.h
index 47ce01bd0c719839e850bde2307b61472c9c5587..fcf558461e08e2be5c4a6234478b1f24827cc552 100644
--- a/src/x64/macro-assembler-x64.h
+++ b/src/x64/macro-assembler-x64.h
@@ -930,6 +930,17 @@ class MacroAssembler: public Assembler {
                                Register scratch2,
                                Label* gc_required);
 
+  // Allocate a raw sliced string object. Only the map field of the result is
+  // initialized.
+  void AllocateSlicedString(Register result,
+                            Register scratch1,
+                            Register scratch2,
+                            Label* gc_required);
+  void AllocateAsciiSlicedString(Register result,
+                                 Register scratch1,
+                                 Register scratch2,
+                                 Label* gc_required);
+
   // ---------------------------------------------------------------------------
   // Support functions.