Make ozone/drm/mojo more immune to startup races

ui/ozone/platform/drm/cursor_proxy_mojo.h

Index: ui/ozone/platform/drm/cursor_proxy_mojo.h
diff --git a/ui/ozone/platform/drm/cursor_proxy_mojo.h b/ui/ozone/platform/drm/cursor_proxy_mojo.h
index 33577aee9ffc5322d09a9148cecc6474ef002179..ccfd6d7009483d79f7794c21e93f090c70d4a444 100644
--- a/ui/ozone/platform/drm/cursor_proxy_mojo.h
+++ b/ui/ozone/platform/drm/cursor_proxy_mojo.h
@@ -8,6 +8,7 @@
 #include "ui/gfx/native_widget_types.h"
 #include "ui/ozone/platform/drm/gpu/inter_thread_messaging_proxy.h"
 #include "ui/ozone/platform/drm/host/drm_cursor.h"
+#include "ui/ozone/platform/drm/host/gpu_thread_observer.h"
 #include "ui/ozone/public/interfaces/device_cursor.mojom.h"
 
 namespace service_manager {
@@ -21,7 +22,7 @@ namespace ui {
 // pointer control via Mojo-style IPC. This code runs only in the mus-ws (i.e.
 // it's the client) and sends mouse pointer control messages to a less
 // priviledged process.
-class CursorProxyMojo : public DrmCursorProxy {
+class CursorProxyMojo : public DrmCursorProxy, public GpuThreadObserver {
  public:
   explicit CursorProxyMojo(service_manager::Connector* connector);
   ~CursorProxyMojo() override;
@@ -35,6 +36,11 @@ class CursorProxyMojo : public DrmCursorProxy {
   void Move(gfx::AcceleratedWidget window, const gfx::Point& point) override;
   void InitializeOnEvdev() override;
 
+  // GpuThreadObserver
+  void OnGpuProcessLaunched() override;
+  void OnGpuThreadReady() override;
+  void OnGpuThreadRetired() override;
+
   std::unique_ptr<service_manager::Connector> connector_;
 
   // Mojo implementation of the DrmCursorProxy.
@@ -42,6 +48,8 @@ class CursorProxyMojo : public DrmCursorProxy {
   ui::ozone::mojom::DeviceCursorPtr evdev_cursor_ptr_;
 
   base::PlatformThreadRef evdev_ref_;
+
+  bool have_gpu_thread_ = false;
 };
 
 }  // namespace ui