Introduce painted-device-scale-factor and use it when --enable-use-zoom-for-dsf is specified.

cc/trees/layer_tree_host.h

Index: cc/trees/layer_tree_host.h
diff --git a/cc/trees/layer_tree_host.h b/cc/trees/layer_tree_host.h
index ab38aba16fdea413981fc9b60ae1291c37ee66af..3f6b533609cf237a4ee3ebeb746703a4c2205ea5 100644
--- a/cc/trees/layer_tree_host.h
+++ b/cc/trees/layer_tree_host.h
@@ -238,6 +238,8 @@ class CC_EXPORT LayerTreeHost : public MutatorHostClient {
   void SetImplTransform(const gfx::Transform& transform);
 
   void SetDeviceScaleFactor(float device_scale_factor);
+  void SetPaintedDeviceScaleFactor(float painted_device_scale_factor);
+
   float device_scale_factor() const { return device_scale_factor_; }
 
   void UpdateTopControlsState(TopControlsState constraints,
@@ -443,6 +445,7 @@ class CC_EXPORT LayerTreeHost : public MutatorHostClient {
   float top_controls_height_;
   float top_controls_shown_ratio_;
   float device_scale_factor_;
+  float painted_device_scale_factor_;
 
   bool visible_;