Pepper uses DIP, so RWFullscreenPepper should always use SetDeviceScaleFctor.

content/renderer/render_widget_fullscreen_pepper.h

 // Copyright (c) 2012 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_RENDERER_RENDER_WIDGET_FULLSCREEN_PEPPER_H_
 #define CONTENT_RENDERER_RENDER_WIDGET_FULLSCREEN_PEPPER_H_
 
 #include <stdint.h>
 
 #include "base/macros.h"
@@ skipping 53 matching lines @@
   void DidInitiatePaint() override;
   void DidFlushPaint() override;
   void Close() override;
   void OnResize(const ResizeParams& params) override;
 
   // RenderWidgetFullscreen API.
   blink::WebWidget* CreateWebWidget() override;
 
   // RenderWidget overrides.
   GURL GetURLForGraphicsContext3D() override;
-  void SetDeviceScaleFactor(float device_scale_factor) override;
+  void OnDeviceScaleFactorChanged() override;
 
  private:
   // URL that is responsible for this widget, passed to ggl::CreateViewContext.
   GURL active_url_;
 
   // The plugin instance this widget wraps.
   PepperPluginInstanceImpl* plugin_;
 
   blink::WebLayer* layer_;
 
   scoped_ptr<MouseLockDispatcher> mouse_lock_dispatcher_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderWidgetFullscreenPepper);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_RENDER_WIDGET_FULLSCREEN_PEPPER_H_