Initialize pre-allocated fields of JSObject with undefined.

src/arm/macro-assembler-arm.h

Index: src/arm/macro-assembler-arm.h
diff --git a/src/arm/macro-assembler-arm.h b/src/arm/macro-assembler-arm.h
index 2709b4fd27c25e49242d70145c2528e6cc84bbf5..02d13df58377eaac1ef64a59632e95f7f51f0a10 100644
--- a/src/arm/macro-assembler-arm.h
+++ b/src/arm/macro-assembler-arm.h
@@ -560,6 +560,13 @@ class MacroAssembler: public Assembler {
                  Register length,
                  Register scratch);
 
+  // Initialize fields with filler values.  Fields starting at |start_offset|
+  // not including end_offset are overwritten with the value in |filler|.  At
+  // the end the loop, |start_offset| takes the value of |end_offset|.
+  void InitializeFieldsWithFiller(Register start_offset,
+                                  Register end_offset,
+                                  Register filler);
+
   // ---------------------------------------------------------------------------
   // Support functions.