ozone: Reject overlays when a test buffer can't be allocated.

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

Index: ui/ozone/platform/drm/gpu/drm_overlay_validator.cc
diff --git a/ui/ozone/platform/drm/gpu/drm_overlay_validator.cc b/ui/ozone/platform/drm/gpu/drm_overlay_validator.cc
index e83d62e6070314de5812d5d556406189c9ed3ad4..f1fb74222d3701701506e351f35f1af126bbdef9 100644
--- a/ui/ozone/platform/drm/gpu/drm_overlay_validator.cc
+++ b/ui/ozone/platform/drm/gpu/drm_overlay_validator.cc
@@ -132,15 +132,14 @@ std::vector<OverlayCheck_Params> DrmOverlayValidator::TestPageFlip(
 
     uint32_t original_format = GetFourCCFormatForFramebuffer(overlay.format);
     scoped_refptr<ScanoutBuffer> buffer =
-        GetBufferForPageFlipTest(drm, scaled_buffer_size, original_format,
+        GetBufferForPageFlipTest(drm, overlay.buffer_size, original_format,
                                  buffer_generator_, &reusable_buffers);
-    DCHECK(buffer);
 
     OverlayPlane plane(buffer, overlay.plane_z_order, overlay.transform,
                        overlay.display_rect, overlay.crop_rect);
     test_list.push_back(plane);
 
-    if (controller->TestPageFlip(test_list)) {
+    if (buffer && controller->TestPageFlip(test_list)) {
       overlay.is_overlay_candidate = true;
 
       // If size scaling is needed, find an optimal format.