Implements core logic for Pixel Canvas

ui/compositor/layer.cc

Index: ui/compositor/layer.cc
diff --git a/ui/compositor/layer.cc b/ui/compositor/layer.cc
index 468789ae00f64bb7f64871499b96cdf62a696a50..49ff13b82d78eedd4bb51612f27e78169018eca6 100644
--- a/ui/compositor/layer.cc
+++ b/ui/compositor/layer.cc
@@ -40,6 +40,10 @@
 namespace {
 
 const ui::Layer* GetRoot(const ui::Layer* layer) {
+  // Parent walk cannot be done on a layer that is being used as a mask. Get the
+  // layer to which this layer is a mask of.
+  if (layer->layer_mask_back_link())
+    layer = layer->layer_mask_back_link();
   while (layer->parent())
     layer = layer->parent();
   return layer;
@@ -933,8 +937,9 @@ scoped_refptr<cc::DisplayItemList> Layer::PaintContentsToDisplayList(
   paint_region_.Clear();
   auto display_list = make_scoped_refptr(new cc::DisplayItemList);
   if (delegate_) {
-    delegate_->OnPaintLayer(
-        PaintContext(display_list.get(), device_scale_factor_, invalidation));
+    delegate_->OnPaintLayer(PaintContext(display_list.get(),
+                                         device_scale_factor_, invalidation,
+                                         GetCompositor()->is_pixel_canvas()));
   }
   display_list->Finalize();
   // TODO(domlaskowski): Move mirror invalidation to Layer::SchedulePaint.