Pass root ServerWindow id to FrameGenerator.

services/ui/ws/display.cc

Index: services/ui/ws/display.cc
diff --git a/services/ui/ws/display.cc b/services/ui/ws/display.cc
index f11f959aa50f8c5a9b92abd93162f39a2f22c028..fc1f161cb3dbe5b86ec2d34b9aad2ba1d998d01b 100644
--- a/services/ui/ws/display.cc
+++ b/services/ui/ws/display.cc
@@ -33,10 +33,13 @@ namespace ui {
 namespace ws {
 
 Display::Display(WindowServer* window_server,
-                 const PlatformDisplayInitParams& platform_display_init_params)
-    : window_server_(window_server),
-      platform_display_(PlatformDisplay::Create(platform_display_init_params)),
-      last_cursor_(mojom::Cursor::CURSOR_NULL) {
+                 PlatformDisplayInitParams init_params)

[Fady Samuel, 2016/10/24 21:53:22]

This is more or less the same in terms of cost, but I generally prefer passing
by const ref, copying locally and updating.

[kylechar, 2016/10/25 18:15:01]

Done.

+    : window_server_(window_server), last_cursor_(mojom::Cursor::CURSOR_NULL) {
+  // Create the root ServerWindow and pass the window id along.
+  CreateRootWindow(init_params.metrics.bounds.size());
+  init_params.root_window_id = root_->id();
+
+  platform_display_.reset(PlatformDisplay::Create(init_params));
   platform_display_->Init(this);
 
   window_server_->window_manager_window_tree_factory_set()->AddObserver(this);