Disable blink_perf.dom custom element default style story

TBR=crouleau@chromium.org
CC=hayato@chromium.org,tkent@chromium.org

Bug: 914084
Change-Id: I42a62fdb5bb6b7f74291272b4c3d1fc14bfbdbfa
Reviewed-on: https://chromium-review.googlesource.com/c/1372721Reviewed-by: Charlie Andrews <charliea@chromium.org>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Commit-Queue: Charlie Andrews <charliea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615748}

tools/perf/expectations.config

@@ -40,6 +40,9 @@ crbug.com/853738 [ Android_Webview ] blink_perf.canvas/upload-video-to-texture.h
 # Benchmark: blink_perf.css
 crbug.com/891878 [ Nexus5X_Webview ] blink_perf.css/CustomPropertiesVarAlias.html [ Skip ]
 
+# Benchmark: blink_perf.dom
+crbug.com/914084 [ Nexus_5X ] blink_perf.dom/custom-element-default-style.html [ Skip ]
+
 # Benchmark: blink_perf.layout
 crbug.com/551950 [ Android_Svelte ] blink_perf.layout/* [ Skip ]
 crbug.com/832686 [ Nexus_5 ] blink_perf.layout/subtree-detaching.html [ Skip ]