Refactored RenderViewImpl/RenderWidget so that the device scale factor gets set in content rather than from Blink.

This is one step to eliminate device scale factor from Blink code.

BUG=485650
TEST=no functional change. All test should pass.

Review URL: https://codereview.chromium.org/1530463005

Cr-Commit-Position: refs/heads/master@{#365561}
diff --git a/content/renderer/render_widget.h b/content/renderer/render_widget.h
index 748482c..d71c16e 100644
--- a/content/renderer/render_widget.h
+++ b/content/renderer/render_widget.h
@@ -445,6 +445,10 @@
   virtual void OnImeConfirmComposition(const base::string16& text,
                                        const gfx::Range& replacement_range,
                                        bool keep_selection);
+  // Called when the device scale factor is changed, or the layer tree is
+  // initialized.
+  virtual void OnDeviceScaleFactorChanged();
+
   void OnRepaint(gfx::Size size_to_paint);
   void OnSyntheticGestureCompleted();
   void OnSetTextDirection(blink::WebTextDirection direction);