Make ozone/drm/mojo more immune to startup races

ui/ozone/platform/drm/gpu/drm_thread.cc

Index: ui/ozone/platform/drm/gpu/drm_thread.cc
diff --git a/ui/ozone/platform/drm/gpu/drm_thread.cc b/ui/ozone/platform/drm/gpu/drm_thread.cc
index 8eaaeee1deb0a83efeccac5a07ad8781784f111c..5aca48d7a8077f5953730b62259880fa9ed0e075 100644
--- a/ui/ozone/platform/drm/gpu/drm_thread.cc
+++ b/ui/ozone/platform/drm/gpu/drm_thread.cc
@@ -207,8 +207,12 @@ void DrmThread::SetCursor(const gfx::AcceleratedWidget& widget,
                           const std::vector<SkBitmap>& bitmaps,
                           const gfx::Point& location,
                           int32_t frame_delay_ms) {
-  screen_manager_->GetWindow(widget)
-      ->SetCursor(bitmaps, location, frame_delay_ms);
+  auto window = screen_manager_->GetWindow(widget);

[sadrul, 2017/05/29 16:50:15]

I think we suggest using 'auto*' here.

+  // TODO(rjkroege): This check is needed only to address mushrome startup

[dnicoara, 2017/05/29 17:01:54]

Why isn't the |drm_thread_| check enough for this case?

I'm more concerned by MoveCursor() since that skips the UI thread.

Wouldn't all window operations need this check?

+  // synchronization issues. Remove as part of http://crbug.com/581462
+  if (!window)
+    return;
+  window->SetCursor(bitmaps, location, frame_delay_ms);
 }
 
 void DrmThread::MoveCursor(const gfx::AcceleratedWidget& widget,