Fix object initialization when slack tracking for it's map is still enabled.

src/x64/macro-assembler-x64.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_X64_MACRO_ASSEMBLER_X64_H_
 #define V8_X64_MACRO_ASSEMBLER_X64_H_
 
 #include "src/assembler.h"
 #include "src/bailout-reason.h"
 #include "src/base/flags.h"
@@ skipping 1455 matching lines @@
   // free, do use it, otherwise kScratchRegister will be used).
   // The min_length is a minimum limit on the value that length will have.
   // The algorithm has some special cases that might be omitted if the string
   // is known to always be long.
   void CopyBytes(Register destination,
                  Register source,
                  Register length,
                  int min_length = 0,
                  Register scratch = kScratchRegister);
 
-  // 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);
+  // Initialize fields with filler values.  Fields starting at |current_address|
+  // not including |end_address| are overwritten with the value in |filler|.  At
+  // the end the loop, |current_address| takes the value of |end_address|.
+  void InitializeFieldsWithFiller(Register current_address,
+                                  Register end_address, Register filler);
 
 
   // Emit code for a truncating division by a constant. The dividend register is
   // unchanged, the result is in rdx, and rax gets clobbered.
   void TruncatingDiv(Register dividend, int32_t divisor);
 
   // ---------------------------------------------------------------------------
   // StatsCounter support
 
   void SetCounter(StatsCounter* counter, int value);
@@ skipping 241 matching lines @@
   }                                                                          \
   masm->
 #else
 #define ACCESS_MASM(masm) masm->
 #endif
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_X64_MACRO_ASSEMBLER_X64_H_