Make ozone/drm/mojo more immune to startup races

ui/ozone/platform/drm/ozone_platform_gbm.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/ozone/platform/drm/ozone_platform_gbm.h"
 
 #include <dlfcn.h>
 #include <fcntl.h>
 #include <gbm.h>
 #include <stdlib.h>
@@ skipping 106 matching lines @@
     if (drm_thread_proxy_)
       drm_thread_proxy_->AddBinding(std::move(request));
     else
       pending_cursor_requests_.push_back(std::move(request));
   }
   std::unique_ptr<PlatformWindow> CreatePlatformWindow(
       PlatformWindowDelegate* delegate,
       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();
     }
 
     std::unique_ptr<DrmWindowHost> platform_window(new DrmWindowHost(
         delegate, bounds, adapter, event_factory_ozone_.get(), cursor_.get(),
         window_manager_.get(), display_manager_.get(), overlay_manager_.get()));
     platform_window->Initialize();
     return std::move(platform_window);
   }
   std::unique_ptr<display::NativeDisplayDelegate> CreateNativeDisplayDelegate()
@@ skipping 130 matching lines @@
   DISALLOW_COPY_AND_ASSIGN(OzonePlatformGbm);
 };
 
 }  // namespace
 
 OzonePlatform* CreateOzonePlatformGbm() {
   return new OzonePlatformGbm;
 }
 
 }  // namespace ui