Realize IWYU pattern for handles.h header.

src/i18n.h

 // Copyright 2013 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.
 // limitations under the License.
 
 #ifndef V8_I18N_H_
 #define V8_I18N_H_
 
 #include "src/handles.h"
 #include "unicode/uversion.h"
 
 namespace U_ICU_NAMESPACE {
 class BreakIterator;
 class Collator;
 class DecimalFormat;
 class SimpleDateFormat;
 }
 
 namespace v8 {
 namespace internal {
 
+// Forward declarations.
+class ObjectTemplateInfo;
+
 class I18N {
  public:
   // Creates an ObjectTemplate with one internal field.
   static Handle<ObjectTemplateInfo> GetTemplate(Isolate* isolate);
 
   // Creates an ObjectTemplate with two internal fields.
   static Handle<ObjectTemplateInfo> GetTemplate2(Isolate* isolate);
 
  private:
   I18N();
@@ skipping 89 matching lines @@
   static void DeleteBreakIterator(
       const v8::WeakCallbackData<v8::Value, void>& data);
 
  private:
   BreakIterator();
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_I18N_H_