ozone: Add an opaque fb to ScanoutBuffer for primary planes.

ui/ozone/platform/drm/common/drm_util.cc

Index: ui/ozone/platform/drm/common/drm_util.cc
diff --git a/ui/ozone/platform/drm/common/drm_util.cc b/ui/ozone/platform/drm/common/drm_util.cc
index 9d41e98adaad16d246b2356d2679130ea1c2ec1e..d4c7487b3f7bdd43281fbc8aa3d6cec52b15ebcd 100644
--- a/ui/ozone/platform/drm/common/drm_util.cc
+++ b/ui/ozone/platform/drm/common/drm_util.cc
@@ -421,8 +421,10 @@ gfx::BufferFormat GetBufferFormatFromFourCCFormat(int format) {
   }
 }
 
-int GetFourCCFormatForFramebuffer(gfx::BufferFormat format) {
-  // Currently, drm supports 24 bitcolordepth for hardware overlay.
+int GetFourCCFormatForOpaqueFramebuffer(gfx::BufferFormat format) {
+  // DRM atomic interface doesn't currently support specifying an alpha
+  // blending. We can simulate disabling alpha bleding creating an fb
+  // with a format without the alpha channel.
   switch (format) {
     case gfx::BufferFormat::RGBA_8888:
     case gfx::BufferFormat::RGBX_8888: