[iwyu] Include handles.h less.

src/field-type.h

 // 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.
 
 #ifndef V8_FIELD_TYPE_H_
 #define V8_FIELD_TYPE_H_
 
 #include "src/ast/ast-types.h"
-#include "src/handles.h"
 #include "src/objects.h"
 #include "src/ostreams.h"
 
 namespace v8 {
 namespace internal {
 
+template <typename T>
+class Handle;
+
 class FieldType : public Object {
  public:
   static FieldType* None();
   static FieldType* Any();
   static Handle<FieldType> None(Isolate* isolate);
   static Handle<FieldType> Any(Isolate* isolate);
   static FieldType* Class(i::Map* map);
   static Handle<FieldType> Class(i::Handle<i::Map> map, Isolate* isolate);
   static FieldType* cast(Object* object);
 
@@ skipping 15 matching lines @@
   bool NowIs(Handle<FieldType> other);
   AstType* Convert(Zone* zone);
 
   void PrintTo(std::ostream& os);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_FIELD_TYPE_H_