ui: Make gfx::Size::Scale() mutate the class. Add gfx::ScaleSize() similar to Rect/Point.

ui/compositor/layer.cc

Index: ui/compositor/layer.cc
diff --git a/ui/compositor/layer.cc b/ui/compositor/layer.cc
index d3dc6ca60993417d74610759cfe3f4ccd165dbe5..2a88db500fe5b74141d8dddd174b02b8638ba6b6 100644
--- a/ui/compositor/layer.cc
+++ b/ui/compositor/layer.cc
@@ -767,8 +767,9 @@ void Layer::RecomputeDrawsContentAndUVRect() {
   } else {
     DCHECK(texture_);
 
+    float texture_scale_factor = 1.0f / texture_->device_scale_factor();
     gfx::Size texture_size = gfx::ToFlooredSize(
-          texture_->size().Scale(1.0f / texture_->device_scale_factor()));
+        gfx::ScaleSize(texture_->size(), texture_scale_factor));
 
     gfx::Size size(std::min(bounds().width(), texture_size.width()),
                    std::min(bounds().height(), texture_size.height()));