Revert "Replace HeapNumber as doublebox with an explicit MutableHeapNumber."

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/frames.h"
 #include "src/globals.h"
@@ skipping 1168 matching lines @@
   // it will no longer be allocated. Make sure that no pointers are left to the
   // object(s) no longer allocated as they would be invalid when allocation is
   // un-done.
   void UndoAllocationInNewSpace(Register object);
 
   // Allocate a heap number in new space with undefined value. Returns
   // tagged pointer in result register, or jumps to gc_required if new
   // space is full.
   void AllocateHeapNumber(Register result,
                           Register scratch,
-                          Label* gc_required,
-                          MutableMode mode = IMMUTABLE);
+                          Label* gc_required);
 
   // Allocate a sequential string. All the header fields of the string object
   // are initialized.
   void AllocateTwoByteString(Register result,
                              Register length,
                              Register scratch1,
                              Register scratch2,
                              Register scratch3,
                              Label* gc_required);
   void AllocateAsciiString(Register result,
@@ skipping 447 matching lines @@
     masm->popfq();                                                           \
   }                                                                          \
   masm->
 #else
 #define ACCESS_MASM(masm) masm->
 #endif
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_MACRO_ASSEMBLER_X64_H_