Implement temporary reference assignment with DisplayCompositor.

services/ui/ws/window_server.cc

Index: services/ui/ws/window_server.cc
diff --git a/services/ui/ws/window_server.cc b/services/ui/ws/window_server.cc
index 3b0446dea15217be18930c59287a6f6f4925ca74..23a218849f779633f7dfe2d093d442a6c97c77f4 100644
--- a/services/ui/ws/window_server.cc
+++ b/services/ui/ws/window_server.cc
@@ -606,6 +606,31 @@ bool WindowServer::IsUserInHighContrastMode(const UserId& user) const {
   return (iter == high_contrast_mode_.end()) ? false : iter->second;
 }
 
+void WindowServer::ClaimTemporaryReference(ServerWindow* window,
+                                           const cc::SurfaceId& surface_id) {
+  const ClientSpecificId window_client_id = window->id().client_id;
+
+  // Find the first parent window owned by a different client. Since it is a
+  // a different client, it will need to have a CompositorFrameSink in order to
+  // embed |window|.
+  ServerWindow* current = window->parent();
+  while (current && current->id().client_id == window_client_id)
+    current = current->parent();
+
+  // The client that embeds |window| is expected to submit a CompositorFrame
+  // that references |surface_id|. Have the parent claim ownership of the
+  // temporary reference to |surface_id|. If the parent client crashes before it
+  // adds a surface reference then the GPU can cleanup temporary references. If
+  // no parent client embeds |window| then tell the GPU to drop the temporary
+  // reference immediately.
+  if (current) {
+    current->GetOrCreateCompositorFrameSinkManager()->ClaimTemporaryReference(
+        surface_id);
+  } else {
+    display_compositor_->DropTemporaryReference(surface_id);
+  }
+}
+
 ServerWindow* WindowServer::GetRootWindow(const ServerWindow* window) {
   Display* display = display_manager_->GetDisplayContaining(window);
   return display ? display->root_window() : nullptr;
@@ -770,8 +795,6 @@ void WindowServer::OnTransientWindowRemoved(ServerWindow* window,
 }
 
 void WindowServer::OnGpuServiceInitialized() {
-  // TODO(kylechar): When gpu channel is removed, this can instead happen
-  // earlier, after GpuHost::OnInitialized().
   delegate_->StartDisplayInit();
 }
 
@@ -779,16 +802,25 @@ void WindowServer::OnSurfaceCreated(const cc::SurfaceInfo& surface_info) {
   WindowId window_id(
       WindowIdFromTransportId(surface_info.id().frame_sink_id().client_id()));
   ServerWindow* window = GetWindow(window_id);
+
   // If the window doesn't have a parent then we have nothing to propagate.
-  if (!window)
+  if (!window) {
+    display_compositor_->DropTemporaryReference(surface_info.id());
     return;
+  }
 
-  // FrameGenerator will add an appropriate reference for the new surface.
   DCHECK(display_manager_->GetDisplayContaining(window));
   auto* display = display_manager_->GetDisplayContaining(window);
   if (window == display->GetActiveRootWindow()) {
+    // FrameGenerator will add an appropriate reference for the new surface.
     display->platform_display()->GetFrameGenerator()->OnSurfaceCreated(
         surface_info);
+
+    display->root_window()
+        ->GetOrCreateCompositorFrameSinkManager()
+        ->ClaimTemporaryReference(surface_info.id());
+  } else {
+    ClaimTemporaryReference(window, surface_info.id());

[Fady Samuel, 2017/03/01 16:07:46]

Can't we generalize this to be a single code path for ClaimTemporaryReference?

[Fady Samuel, 2017/03/01 17:08:27]

Or at least add a comment explaining why this is a special case.

[kylechar, 2017/03/01 17:15:23]

I'll add a comment with why. The client_id doesn't change from display root
(0:2) to the WM root (0:3) like it does for other clients.

   }
 
   // This is only used for testing to observe that a window has a