Initialize pre-allocated fields of JSObject with undefined.

src/ia32/macro-assembler-ia32.cc

Index: src/ia32/macro-assembler-ia32.cc
diff --git a/src/ia32/macro-assembler-ia32.cc b/src/ia32/macro-assembler-ia32.cc
index b9362a0226b5967cb514c2b37679583981031656..0bb074b9ba94ded195ba62e9e5f59083ea7f82f8 100644
--- a/src/ia32/macro-assembler-ia32.cc
+++ b/src/ia32/macro-assembler-ia32.cc
@@ -1294,6 +1294,20 @@ void MacroAssembler::CopyBytes(Register source,
 }
 
 
+void MacroAssembler::InitializeFieldsWithFiller(Register start_offset,
+                                                Register end_offset,
+                                                Register filler) {
+  Label loop, entry;
+  jmp(&entry);
+  bind(&loop);
+  mov(Operand(start_offset, 0), filler);
+  add(Operand(start_offset), Immediate(kPointerSize));
+  bind(&entry);
+  cmp(start_offset, Operand(end_offset));
+  j(less, &loop);
+}
+
+
 void MacroAssembler::NegativeZeroTest(Register result,
                                       Register op,
                                       Label* then_label) {