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 df0cb0a2d8b04471226174852b8a0d78d91cb5bb..896f84721e096208bfb8578bb0f5888815632739 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();
     }