Add subpixel-offset attribute to layer attirbute view.

Bug: None

Change-Id: I699335142351d8a33e031db7d8d921536d06a3e8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2336496Reviewed-by: Wei Li <weili@chromium.org>
Commit-Queue: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#794734}

components/ui_devtools/views/element_utility.cc

@@ -31,6 +31,9 @@ void AppendLayerPropertiesMatchedStyle(
                     base::NumberToString(layer->layer_brightness()));
   ret->emplace_back("layer-grayscale",
                     base::NumberToString(layer->layer_grayscale()));
+  const auto offset = layer->GetSubpixelOffset();
+  if (!offset.IsZero())
+    ret->emplace_back("layer-subpixel-offset", offset.ToString());
   const ui::Layer::ShapeRects* alpha_shape_bounds = layer->alpha_shape();
   if (alpha_shape_bounds && alpha_shape_bounds->size()) {
     gfx::Rect bounding_box;