content: Cleanup class/struct forward declarations

content/browser/android/date_time_chooser_android.h

 // Copyright (c) 2013 The Chromium 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 CONTENT_BROWSER_ANDROID_DATE_TIME_CHOOSER_ANDROID_H_
 #define CONTENT_BROWSER_ANDROID_DATE_TIME_CHOOSER_ANDROID_H_
 
 #include <memory>
 #include <string>
 #include <vector>
 
 #include "base/android/jni_weak_ref.h"
 #include "base/macros.h"
 #include "ui/base/ime/text_input_type.h"
 #include "ui/gfx/native_widget_types.h"
 
 namespace content {
 
-class ContentViewCore;
 class RenderViewHost;
 struct DateTimeSuggestion;
 
 // Android implementation for DateTimeChooser dialogs.
 class DateTimeChooserAndroid {
  public:
   DateTimeChooserAndroid();
   ~DateTimeChooserAndroid();
 
   // DateTimeChooser implementation:
@@ skipping 23 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(DateTimeChooserAndroid);
 };
 
 // Native JNI methods
 bool RegisterDateTimeChooserAndroid(JNIEnv* env);
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_ANDROID_DATE_TIME_CHOOSER_ANDROID_H_