cc: Use ScreenSpaceTransform to determine content scale

cc/layers/layer_impl.cc

Index: cc/layers/layer_impl.cc
diff --git a/cc/layers/layer_impl.cc b/cc/layers/layer_impl.cc
index 1d373eec763070f7f5ed7c6f52d3a11a44f46eb9..f27ad1e02e3cb173cfe69ec22ee3202af5bc6231 100644
--- a/cc/layers/layer_impl.cc
+++ b/cc/layers/layer_impl.cc
@@ -1399,7 +1399,7 @@ float LayerImpl::GetIdealContentsScale() const {
   }
 
   gfx::Vector2dF transform_scales = MathUtil::ComputeTransform2dScaleComponents(
-      DrawTransform(), default_scale);
+      ScreenSpaceTransform(), default_scale);
   return std::max(transform_scales.x(), transform_scales.y());
 }