Pepper uses DIP, so RWFullscreenPepper should always use SetDeviceScaleFctor.

content/renderer/render_widget_fullscreen_pepper.cc

Index: content/renderer/render_widget_fullscreen_pepper.cc
diff --git a/content/renderer/render_widget_fullscreen_pepper.cc b/content/renderer/render_widget_fullscreen_pepper.cc
index e751afdfc2a7c6ff2c23ffe95d578aa719bae052..d75b2796240c7290effd3f8c2e6f062437dbf32d 100644
--- a/content/renderer/render_widget_fullscreen_pepper.cc
+++ b/content/renderer/render_widget_fullscreen_pepper.cc
@@ -384,11 +384,9 @@ GURL RenderWidgetFullscreenPepper::GetURLForGraphicsContext3D() {
   return active_url_;
 }
 
-void RenderWidgetFullscreenPepper::SetDeviceScaleFactor(
-    float device_scale_factor) {
-  RenderWidget::SetDeviceScaleFactor(device_scale_factor);
+void RenderWidgetFullscreenPepper::OnDeviceScaleFactorChanged() {
   if (compositor_)
-    compositor_->setDeviceScaleFactor(device_scale_factor);
+    compositor_->setDeviceScaleFactor(device_scale_factor_);
 }
 
 }  // namespace content