Pretenure ASCII cons string in high promotion mode.

src/arm/macro-assembler-arm.cc

Index: src/arm/macro-assembler-arm.cc
diff --git a/src/arm/macro-assembler-arm.cc b/src/arm/macro-assembler-arm.cc
index bae50600268ae4fc46524a75395b6a32b621a2d2..e625606663f2f11b19a3d1e4b8f6fdc9186e5f19 100644
--- a/src/arm/macro-assembler-arm.cc
+++ b/src/arm/macro-assembler-arm.cc
@@ -1933,8 +1933,34 @@ void MacroAssembler::AllocateAsciiConsString(Register result,
                                              Register scratch1,
                                              Register scratch2,
                                              Label* gc_required) {
-  Allocate(ConsString::kSize, result, scratch1, scratch2, gc_required,
-           TAG_OBJECT);
+  Label allocate_new_space, install_map;
+  AllocationFlags flags = TAG_OBJECT;
+
+  ExternalReference high_promotion_mode = ExternalReference::
+      new_space_high_promotion_mode_active_address(isolate());
+  mov(scratch1, Operand(high_promotion_mode));
+  ldr(scratch1, MemOperand(r4, 0));
+  cmp(scratch1, Operand::Zero());
+  b(eq, &allocate_new_space);
+
+  Allocate(ConsString::kSize,
+           result,
+           scratch1,
+           scratch2,
+           gc_required,
+           static_cast<AllocationFlags>(flags | PRETENURE_OLD_POINTER_SPACE));
+
+  jmp(&install_map);
+
+  bind(&allocate_new_space);
+  Allocate(ConsString::kSize,
+           result,
+           scratch1,
+           scratch2,
+           gc_required,
+           flags);
+
+  bind(&install_map);
 
   InitializeNewString(result,
                       length,