Views: Remove disabled SetCustomMask() on NativeViewHost for Windows

This re-enabled SetCustomMask() on NativeViewHostAura for Windows as
the layer related scaling bug has since been fixed.

Bug: 843250, 863268
Change-Id: If7b9e61e6913143e415f0af20e05d7dab91ef665
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2366153Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Thomas Lukaszewicz <tluk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#800339}

ui/views/controls/native/native_view_host_aura.cc

@@ -161,18 +161,12 @@ void NativeViewHostAura::RemovedFromWidget() {
 }
 
 bool NativeViewHostAura::SetCustomMask(std::unique_ptr<ui::LayerOwner> mask) {
-#if defined(OS_WIN)
-  // TODO(crbug/843250): On Aura, layer masks don't play with HiDPI. Fix this
-  // and enable this on Windows.
-  return false;
-#else
   UninstallMask();
   mask_ = std::move(mask);
   if (mask_)
     mask_->layer()->SetFillsBoundsOpaquely(false);
   InstallMask();
   return true;
-#endif
 }
 
 void NativeViewHostAura::SetHitTestTopInset(int top_inset) {