Reland r22082 "Replace HeapNumber as doublebox with an explicit MutableHeapNumber."

src/x87/macro-assembler-x87.cc

Index: src/x87/macro-assembler-x87.cc
diff --git a/src/x87/macro-assembler-x87.cc b/src/x87/macro-assembler-x87.cc
index c549668038158496da82dd4ea39456977d5d258b..65682b855c843133a4f2adf40c50c68602d772c3 100644
--- a/src/x87/macro-assembler-x87.cc
+++ b/src/x87/macro-assembler-x87.cc
@@ -1576,14 +1576,18 @@ void MacroAssembler::UndoAllocationInNewSpace(Register object) {
 void MacroAssembler::AllocateHeapNumber(Register result,
                                         Register scratch1,
                                         Register scratch2,
-                                        Label* gc_required) {
+                                        Label* gc_required,
+                                        MutableMode mode) {
   // Allocate heap number in new space.
   Allocate(HeapNumber::kSize, result, scratch1, scratch2, gc_required,
            TAG_OBJECT);
 
+  Handle<Map> map = mode == MUTABLE
+      ? isolate()->factory()->mutable_heap_number_map()
+      : isolate()->factory()->heap_number_map();
+
   // Set the map.
-  mov(FieldOperand(result, HeapObject::kMapOffset),
-      Immediate(isolate()->factory()->heap_number_map()));
+  mov(FieldOperand(result, HeapObject::kMapOffset), Immediate(map));
 }