Disable rendering.mobile/cnn_mobile_pinch_2018 on webview

The story hasn't passed reliably since 3/26.

NOTRY=true
TBR=vmiura@chromium.org,sadrul@chromium.org

Bug: 954948
Change-Id: I0f2dc1cb5f372dc5cbe9607897de189f65965ae2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1576153Reviewed-by: Charlie Andrews <charliea@chromium.org>
Commit-Queue: Charlie Andrews <charliea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#652844}

tools/perf/expectations.config

@@ -214,6 +214,7 @@ crbug.com/910207 [ Nexus_5X ] rendering.mobile/yahoo_news_2018 [ Skip ]
 crbug.com/901526 [ All ] rendering.mobile/microsoft_fireflies [ Skip ]
 crbug.com/924400 [ Nexus6_Webview ] rendering.mobile/canvas_animation_no_clear [ Skip ]
 crbug.com/949366 [ Nexus5X_Webview ] rendering.mobile/google_news_mobile_2018 [ Skip ]
+crbug.com/954948 [ Android_Webview ] rendering.mobile/cnn_mobile_pinch_2018 [ Skip ]
 
 # Benchmark: rasterize_and_record_micro.top_25
 crbug.com/764543 [ All ] rasterize_and_record_micro.top_25/file://static_top_25/wikipedia.html [ Skip ]