Views a11y: Implement AXPlatformNode::FromNativeViewAccessible on all platforms.

ui/views/accessibility/native_view_accessibility_mac.h

 // Copyright 2017 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 UI_VIEWS_ACCESSIBILITY_NATIVE_VIEW_ACCESSIBILITY_MAC_H_
 #define UI_VIEWS_ACCESSIBILITY_NATIVE_VIEW_ACCESSIBILITY_MAC_H_
 
 #include "base/macros.h"
 #include "ui/views/accessibility/native_view_accessibility.h"
 
 namespace views {
 
 // Mac-specific accessibility class for NativeViewAccessibility.
 class NativeViewAccessibilityMac : public NativeViewAccessibility {
  public:
   explicit NativeViewAccessibilityMac(View* view);
 
+ protected:
   // NativeViewAccessibility:
-  gfx::NativeViewAccessible GetParent() override;
+  gfx::NativeViewAccessible GetNativeViewAccessibleForWidget() override;
 
+ private:
   DISALLOW_COPY_AND_ASSIGN(NativeViewAccessibilityMac);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_ACCESSIBILITY_NATIVE_VIEW_ACCESSIBILITY_MAC_H_