Make ozone/drm/mojo more immune to startup races

ui/ozone/platform/drm/ozone_platform_gbm.cc

Index: ui/ozone/platform/drm/ozone_platform_gbm.cc
diff --git a/ui/ozone/platform/drm/ozone_platform_gbm.cc b/ui/ozone/platform/drm/ozone_platform_gbm.cc
index 1ae295d777fd4b1d1a6af312d4aec95f9e35e65d..a324681b57500e657d247285bbc2abee1e91b63f 100644
--- a/ui/ozone/platform/drm/ozone_platform_gbm.cc
+++ b/ui/ozone/platform/drm/ozone_platform_gbm.cc
@@ -124,8 +124,6 @@ class OzonePlatformGbm : public OzonePlatform {
       const gfx::Rect& bounds) override {
     GpuThreadAdapter* adapter = gpu_platform_support_host_.get();
     if (using_mojo_ || single_process_) {
-      DCHECK(drm_thread_proxy_)
-          << "drm_thread_proxy_ should exist (and be running) here.";
       adapter = mus_thread_proxy_.get();
     }
 
@@ -176,15 +174,13 @@ class OzonePlatformGbm : public OzonePlatform {
       gl_api_loader_.reset(new GlApiLoader());
 
     if (using_mojo_) {
-      DCHECK(args.connector);
-      mus_thread_proxy_.reset(new MusThreadProxy());
+      mus_thread_proxy_ =
+          base::MakeUnique<MusThreadProxy>(cursor_.get(), args.connector);
       adapter = mus_thread_proxy_.get();
-      cursor_->SetDrmCursorProxy(new CursorProxyMojo(args.connector));
     } else if (single_process_) {
-      mus_thread_proxy_.reset(new MusThreadProxy());
+      mus_thread_proxy_ =
+          base::MakeUnique<MusThreadProxy>(cursor_.get(), nullptr);
       adapter = mus_thread_proxy_.get();
-      cursor_->SetDrmCursorProxy(
-          new CursorProxyThread(mus_thread_proxy_.get()));
     } else {
       gpu_platform_support_host_.reset(
           new DrmGpuPlatformSupportHost(cursor_.get()));