Fix black screen when switching primary display without bounds change

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 3dfc9d6904ed7ad94962ed641fcc200979d9ce6d..51a2f9c5b5978896140908fddc57f81d82eea119 100644
--- a/ui/ozone/platform/drm/gpu/drm_window.cc
+++ b/ui/ozone/platform/drm/gpu/drm_window.cc
@@ -123,6 +123,16 @@ void DrmWindow::MoveCursor(const gfx::Point& location) {
 
 void DrmWindow::SchedulePageFlip(const std::vector<OverlayPlane>& planes,
                                  const SwapCompletionCallback& callback) {
+  if (controller_) {
+    const DrmDevice* drm = controller_->GetAllocationDrmDevice().get();
+    for (const auto& plane : planes) {
+      if (plane.buffer && plane.buffer->GetDrmDevice() != drm) {

[dnicoara, 2016/05/06 19:17:21]

If I understood this correctly this is only required because there may be
in-flight buffers. Could you please add a comment mentioning this. At first this
isn't obvious since |force_buffer_reallocation_| is set to true during the
window bounds update.

[hshi, 2016/05/06 19:22:31]

Done.

+        force_buffer_reallocation_ = true;
+        break;
+      }
+    }
+  }
+
   if (force_buffer_reallocation_) {
     force_buffer_reallocation_ = false;
     callback.Run(gfx::SwapResult::SWAP_NAK_RECREATE_BUFFERS);