Disable flaky loading tests on win 10 perf config

NOTRY=true
TBR=kouhei@chromium.org, ksakamoto@chromium.org

Bug: 876636, 879833
Change-Id: I6d2963cbc6ca33da5e62e68a17d19330786f864a
Reviewed-on: https://chromium-review.googlesource.com/1208960Reviewed-by: Ned Nguyen <nednguyen@google.com>
Commit-Queue: Ned Nguyen <nednguyen@google.com>
Cr-Commit-Position: refs/heads/master@{#589076}

tools/perf/expectations.config

@@ -56,8 +56,10 @@ crbug.com/752611 [ Linux ] loading.desktop/uol.com.br_warm [ Skip ]
 crbug.com/867836 [ All ] loading.desktop/Elmundo_warm [ Skip ]
 crbug.com/876636 [ ChromeOS ] loading.desktop/TheOnion_cold [ Skip ]
 crbug.com/876636 [ ChromeOS ] loading.desktop/TheOnion_warm [ Skip ]
+crbug.com/876636 [ Win_10 ] loading.desktop/TheOnion_warm [ Skip ]
 crbug.com/876636 [ ChromeOS ] loading.desktop/AllRecipes_warm [ Skip ]
 crbug.com/879833 [ Mac_10.12 ] loading.desktop/AllRecipes_cold [ Skip ]
+crbug.com/879833 [ Win_10 ] loading.desktop/AllRecipes_cold [ Skip ]
 
 # Benchmark: loading.mobile
 crbug.com/656861 [ All ] loading.mobile/G1 [ Skip ]