[Refactor] Introduce MediaDelegate

ash/accessibility_delegate.h

 // Copyright 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 ASH_ACCESSIBILITY_DELEGATE_H_
 #define ASH_ACCESSIBILITY_DELEGATE_H_
 
 #include "ash/ash_export.h"
 #include "ash/magnifier/magnifier_constants.h"
 
 namespace ash {
 
 enum AccessibilityNotificationVisibility {
   A11Y_NOTIFICATION_NONE,
   A11Y_NOTIFICATION_SHOW,
 };
 
 // A deletate class to control accessibility features.
 class ASH_EXPORT AccessibilityDelegate {
  public:
-  AccessibilityDelegate() {}
   virtual ~AccessibilityDelegate() {}
 
   // Invoked to toggle spoken feedback for accessibility
   virtual void ToggleSpokenFeedback(
       AccessibilityNotificationVisibility notify) = 0;
 
   // Returns true if spoken feedback is enabled.
   virtual bool IsSpokenFeedbackEnabled() const = 0;
 
   // Invoked to toggle high contrast mode for accessibility.
@@ skipping 37 matching lines @@
   virtual void SaveScreenMagnifierScale(double scale) = 0;
 
   // Gets a saved value of the zoom scale of full screen magnifier. If a value
   // is not saved, return a negative value.
   virtual double GetSavedScreenMagnifierScale() = 0;
 };
 
 }  // namespace ash
 
 #endif  // ASH_ACCESSIBILITYDELEGATE_H_