Switch DRM platform to using a separate thread

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

Index: ui/ozone/platform/drm/gpu/drm_window.cc
diff --git a/ui/ozone/platform/drm/gpu/drm_window.cc b/ui/ozone/platform/drm/gpu/drm_window.cc
index baaeda221a6a5567b8fd1b7356f79f5a71ca1a17..8af203487e7920205394e552f40294d8fb62eb64 100644
--- a/ui/ozone/platform/drm/gpu/drm_window.cc
+++ b/ui/ozone/platform/drm/gpu/drm_window.cc
@@ -126,26 +126,26 @@ void DrmWindow::QueueOverlayPlane(const OverlayPlane& plane) {
   pending_planes_.push_back(plane);
 }
 
-bool DrmWindow::SchedulePageFlip(const SwapCompletionCallback& callback) {
+void DrmWindow::SchedulePageFlip(const SwapCompletionCallback& callback) {
   if (force_buffer_reallocation_) {
     // Clear pending planes otherwise the next call to queue planes will just
     // add on top.
     pending_planes_.clear();
     force_buffer_reallocation_ = false;
     callback.Run(gfx::SwapResult::SWAP_NAK_RECREATE_BUFFERS);
-    return true;
+    return;
   }
 
   last_submitted_planes_.clear();
   last_submitted_planes_.swap(pending_planes_);
 
   if (controller_) {
-    return controller_->SchedulePageFlip(last_submitted_planes_,
-                                         false /* test_only */, callback);
+    if (!controller_->SchedulePageFlip(last_submitted_planes_,
+                                       false /* test_only */, callback))
+      callback.Run(gfx::SwapResult::SWAP_FAILED);
+  } else {
+    callback.Run(gfx::SwapResult::SWAP_ACK);
   }
-
-  callback.Run(gfx::SwapResult::SWAP_ACK);
-  return true;
 }
 
 bool DrmWindow::TestPageFlip(const std::vector<OverlayCheck_Params>& overlays,