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

cc/trees/layer_tree_impl.h

Index: cc/trees/layer_tree_impl.h
diff --git a/cc/trees/layer_tree_impl.h b/cc/trees/layer_tree_impl.h
index 6d544387ff94b6667ecb4d17b4bf82b98c1d55b7..e8257b1df66089eba6fc88c8133608acd8795511 100644
--- a/cc/trees/layer_tree_impl.h
+++ b/cc/trees/layer_tree_impl.h
@@ -199,6 +199,13 @@ class CC_EXPORT LayerTreeImpl {
   void SetDeviceScaleFactor(float device_scale_factor);
   float device_scale_factor() const { return device_scale_factor_; }
 
+  void set_painted_device_scale_factor(float painted_device_scale_factor) {
+    painted_device_scale_factor_ = painted_device_scale_factor;
+  }
+  float painted_device_scale_factor() const {
+    return painted_device_scale_factor_;
+  }
+
   SyncedElasticOverscroll* elastic_overscroll() {
     return elastic_overscroll_.get();
   }
@@ -438,6 +445,7 @@ class CC_EXPORT LayerTreeImpl {
   float max_page_scale_factor_;
 
   float device_scale_factor_;
+  float painted_device_scale_factor_;
 
   scoped_refptr<SyncedElasticOverscroll> elastic_overscroll_;