[stubs] Use CSA::IsHeapNumberMap() instead of manual map comparing.

src/builtins/builtins-conversion.cc

 // Copyright 2016 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/builtins/builtins.h"
 #include "src/builtins/builtins-utils.h"
 #include "src/code-factory.h"
 
 namespace v8 {
 namespace internal {
@@ skipping 166 matching lines @@
 
   Label not_string(&assembler);
   assembler.GotoUnless(assembler.IsStringInstanceType(input_instance_type),
                        &not_string);
   assembler.Return(input);
 
   Label not_heap_number(&assembler);
 
   assembler.Bind(&not_string);
   {
-    assembler.GotoUnless(
-        assembler.WordEqual(input_map, assembler.HeapNumberMapConstant()),
-        &not_heap_number);
+    assembler.GotoUnless(assembler.IsHeapNumberMap(input_map),
+                         &not_heap_number);
     assembler.Goto(&is_number);
   }
 
   assembler.Bind(&is_number);
   { assembler.Return(assembler.NumberToString(context, input)); }
 
   assembler.Bind(&not_heap_number);
   {
     assembler.GotoIf(
         assembler.Word32NotEqual(input_instance_type,
@@ skipping 282 matching lines @@
   CodeStubAssembler assembler(state);
 
   Node* object = assembler.Parameter(Descriptor::kObject);
   Node* context = assembler.Parameter(Descriptor::kContext);
 
   assembler.Return(assembler.Typeof(object, context));
 }
 
 }  // namespace internal
 }  // namespace v8