ozone: support gfx::BufferFormat::RGBX_8888 as a native pixmap format.

ui/ozone/platform/drm/gpu/gbm_buffer.h

Index: ui/ozone/platform/drm/gpu/gbm_buffer.h
diff --git a/ui/ozone/platform/drm/gpu/gbm_buffer.h b/ui/ozone/platform/drm/gpu/gbm_buffer.h
index d80c56bfda1ffbe56be43dbb60935f2c43d904f4..2be65dda871734260230a9f0d683a85bfb5008e6 100644
--- a/ui/ozone/platform/drm/gpu/gbm_buffer.h
+++ b/ui/ozone/platform/drm/gpu/gbm_buffer.h
@@ -26,14 +26,17 @@ class GbmBuffer : public GbmBufferBase {
       gfx::BufferFormat format,
       const gfx::Size& size,
       gfx::BufferUsage usage);
+  gfx::BufferFormat GetFormat() const { return format_; }
   gfx::BufferUsage GetUsage() const { return usage_; }
 
  private:
   GbmBuffer(const scoped_refptr<GbmDevice>& gbm,
             gbm_bo* bo,
+            gfx::BufferFormat format,
             gfx::BufferUsage usage);
   ~GbmBuffer() override;
 
+  gfx::BufferFormat format_;
   gfx::BufferUsage usage_;
 
   DISALLOW_COPY_AND_ASSIGN(GbmBuffer);