ozone: Advertise a top-left origin for GbmSurfaceless

Enabling SkiaRenderer on Chrome OS currently fails a DCHECK [1] that
asserts the backing GLSurface has a top-left origin. Since
GetOrigin() returns the OS presentation API's origin, GbmSurfaceless
should also return a top-left origin. For example, if you call
gbm_bo_map with (x = 0, y = 0), the returned data pointer will
correspond to the top-left of the buffer.

[1] https://source.chromium.org/chromium/chromium/src/+/master:components/viz/service/display_embedder/output_presenter_gl.cc;l=223;drc=238120617b24d1856e0d66e2a6d3272a5e94f658

Change-Id: I0cdfa9d3414cb844dc33470c6342a3a944074d09
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2511879Reviewed-by: Daniele Castagna <dcastagna@chromium.org>
Reviewed-by: Peng Huang <penghuang@chromium.org>
Commit-Queue: Brian Ho <hob@chromium.org>
Cr-Commit-Position: refs/heads/master@{#824399}

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

@@ -215,6 +215,10 @@ void GbmSurfaceless::SetForceGlFlushOnSwapBuffers() {
   requires_gl_flush_on_swap_buffers_ = true;
 }
 
+gfx::SurfaceOrigin GbmSurfaceless::GetOrigin() const {
+  return gfx::SurfaceOrigin::kTopLeft;
+}
+
 GbmSurfaceless::~GbmSurfaceless() {
   Destroy();  // The EGL surface must be destroyed before SurfaceOzone.
   surface_factory_->UnregisterSurface(window_->widget());

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

@@ -72,6 +72,7 @@ class GbmSurfaceless : public gl::SurfacelessEGL {
   EGLConfig GetConfig() override;
   void SetRelyOnImplicitSync() override;
   void SetForceGlFlushOnSwapBuffers() override;
+  gfx::SurfaceOrigin GetOrigin() const override;
 
  protected:
   ~GbmSurfaceless() override;