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

src/mips/stub-cache-mips.cc

 // 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.
 
 #include "src/v8.h"
 
 #if V8_TARGET_ARCH_MIPS
 
 #include "src/codegen.h"
 #include "src/ic-inl.h"
@@ skipping 395 matching lines @@
         if (it.Done()) {
           __ Branch(miss_label, ne, scratch1, Operand(current));
           break;
         }
         __ Branch(&do_store, eq, scratch1, Operand(current));
       }
       __ bind(&do_store);
     }
   } else if (representation.IsDouble()) {
     Label do_store, heap_number;
-    __ LoadRoot(scratch3, Heap::kMutableHeapNumberMapRootIndex);
-    __ AllocateHeapNumber(storage_reg, scratch1, scratch2, scratch3, slow,
-                          TAG_RESULT, MUTABLE);
+    __ LoadRoot(scratch3, Heap::kHeapNumberMapRootIndex);
+    __ AllocateHeapNumber(storage_reg, scratch1, scratch2, scratch3, slow);
 
     __ JumpIfNotSmi(value_reg, &heap_number);
     __ SmiUntag(scratch1, value_reg);
     __ mtc1(scratch1, f6);
     __ cvt_d_w(f4, f6);
     __ jmp(&do_store);
 
     __ bind(&heap_number);
     __ CheckMap(value_reg, scratch1, Heap::kHeapNumberMapRootIndex,
                 miss_label, DONT_DO_SMI_CHECK);
@@ skipping 1078 matching lines @@
   // -----------------------------------
   TailCallBuiltin(masm, Builtins::kKeyedLoadIC_Miss);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_MIPS