ui: Add gfx::BufferUsage::SCANOUT_CPU_READ_WRITE.

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 479e1a2ddc0d3ccc229c53621b164726ed838eda..8faec763cd90274d9e041a76a93b5e60b759aeea 100644
--- a/ui/ozone/platform/drm/gpu/drm_thread.cc
+++ b/ui/ozone/platform/drm/gpu/drm_thread.cc
@@ -117,6 +117,9 @@ void DrmThread::CreateBuffer(gfx::AcceleratedWidget widget,
     case gfx::BufferUsage::SCANOUT:
       flags = GBM_BO_USE_SCANOUT | GBM_BO_USE_RENDERING;
       break;
+    case gfx::BufferUsage::SCANOUT_CPU_READ_WRITE:
+      flags = GBM_BO_USE_SCANOUT | GBM_BO_USE_LINEAR;
+      break;
     case gfx::BufferUsage::GPU_READ_CPU_READ_WRITE:
     case gfx::BufferUsage::GPU_READ_CPU_READ_WRITE_PERSISTENT:
       flags = GBM_BO_USE_LINEAR;