[sheriff] Disable ParkableStringTest.OnlyOneAgingTask

TBR=eirage@chromium.org
NOTRY=true

Bug: 1168170
Change-Id: I675d070a129826054f285085ff1f6771caa3a1bb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2636839Reviewed-by: Xida Chen <xidachen@chromium.org>
Reviewed-by: Ella Ge <eirage@chromium.org>
Commit-Queue: Xida Chen <xidachen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#844810}

third_party/blink/renderer/platform/bindings/parkable_string_test.cc

@@ -986,7 +986,8 @@ TEST_F(ParkableStringTest, AgingTicksStopsWithNoProgress) {
   CheckOnlyCpuCostTaskRemains();
 }
 
-TEST_F(ParkableStringTest, OnlyOneAgingTask) {
+// Flaky on a few platforms: crbug.com/1168170.
+TEST_F(ParkableStringTest, DISABLED_OnlyOneAgingTask) {
   ParkableString parkable1(MakeLargeString('a').ReleaseImpl());
   ParkableString parkable2(MakeLargeString('b').ReleaseImpl());