Move FrameSink hierarchy registration to DisplayCompositor interface

services/ui/ws/server_window.cc

Index: services/ui/ws/server_window.cc
diff --git a/services/ui/ws/server_window.cc b/services/ui/ws/server_window.cc
index b1e6573366f11ca5cf780464a4cf7069c63d7613..9c5bce01942d101a8c69460a44de9624c25a48cc 100644
--- a/services/ui/ws/server_window.cc
+++ b/services/ui/ws/server_window.cc
@@ -26,6 +26,7 @@ ServerWindow::ServerWindow(ServerWindowDelegate* delegate,
                            const Properties& properties)
     : delegate_(delegate),
       id_(id),
+      frame_sink_id_(WindowIdToTransportId(id), 0),
       parent_(nullptr),
       stacking_target_(nullptr),
       transient_parent_(nullptr),
@@ -117,18 +118,12 @@ void ServerWindow::Add(ServerWindow* child) {
   for (auto& observer : child->observers_)
     observer.OnWillChangeWindowHierarchy(child, this, old_parent);
 
-  ServerWindow* old_root = child->GetRoot();
-  ServerWindow* new_root = GetRoot();
-
   if (child->parent())
     child->parent()->RemoveImpl(child);
 
   child->parent_ = this;
   children_.push_back(child);
 
-  if (old_root != new_root)
-    child->ProcessRootChanged(old_root, new_root);
-
   // Stack the child properly if it is a transient child of a sibling.
   if (child->transient_parent_ && child->transient_parent_->parent() == this)
     RestackTransientDescendants(child->transient_parent_, &GetStackingTarget,
@@ -149,9 +144,6 @@ void ServerWindow::Remove(ServerWindow* child) {
 
   RemoveImpl(child);
 
-  if (GetRoot() != nullptr)
-    child->ProcessRootChanged(GetRoot(), nullptr);
-
   // Stack the child properly if it is a transient child of a sibling.
   if (child->transient_parent_ && child->transient_parent_->parent() == this)
     RestackTransientDescendants(child->transient_parent_, &GetStackingTarget,
@@ -431,14 +423,6 @@ void ServerWindow::RemoveImpl(ServerWindow* window) {
   children_.erase(std::find(children_.begin(), children_.end(), window));
 }
 
-void ServerWindow::ProcessRootChanged(ServerWindow* old_root,
-                                      ServerWindow* new_root) {
-  if (compositor_frame_sink_manager_)
-    compositor_frame_sink_manager_->OnRootChanged(old_root, new_root);
-  for (ServerWindow* child : children_)
-    child->ProcessRootChanged(old_root, new_root);
-}
-
 void ServerWindow::OnStackingChanged() {
   if (stacking_target_) {
     Windows::const_iterator window_i = std::find(