Disable failing loading.mobild/Flipboard_warm_3g on N5x webview.

Bug: 867103
Change-Id: I4130ebfd255a7db799d7a572ddc307267e4edbb7
TBR: charliea@chromium.org
NOTRY: true
Reviewed-on: https://chromium-review.googlesource.com/1148988Reviewed-by: Annie Sullivan <sullivan@chromium.org>
Commit-Queue: Annie Sullivan <sullivan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577693}

tools/perf/expectations.config

@@ -112,6 +112,7 @@ crbug.com/859597 [ Nexus_5X ] loading.mobile/GoogleIndonesia_3g [ Skip ]
 crbug.com/859597 [ Nexus_5X ] loading.mobile/QQNews_3g [ Skip ]
 crbug.com/859597 [ Nexus_5X ] loading.mobile/Youtube_3g [ Skip ]
 crbug.com/859597 [ Nexus5X_Webview ] loading.mobile/GoogleBrazil_3g [ Skip ]
+crbug.com/867103 [ Nexus5X_Webview ] loading.mobile/FlipBoard_warm_3g [ Skip ]
 
 # Benchmark: memory.long_running_idle_gmail_tbmv2
 crbug.com/611167 [ Android_Svelte ] memory.long_running_idle_gmail_tbmv2/* [ Skip ]