[sheriff] Disable BackgroundTracingManagerBrowserTest.ReactiveSecondTriggerIgnored

TBR=eirage@chromium.org
NOTRY=true

Bug: 1156793
Change-Id: I7814bd0d0267038f00fbf3cb18230559b6c32d71
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2637399Reviewed-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@{#844804}

content/browser/tracing/background_tracing_manager_browsertest.cc

@@ -1586,8 +1586,9 @@ IN_PROC_BROWSER_TEST_F(BackgroundTracingManagerBrowserTest,
 
 // This tests that reactive mode only terminates with a repeated trigger
 // if the config specifies that it should.
+// Flaky on all major platforms: crbug.com/1156793.
 IN_PROC_BROWSER_TEST_F(BackgroundTracingManagerBrowserTest,
-                       ReactiveSecondTriggerIgnored) {
+                       DISABLED_ReactiveSecondTriggerIgnored) {
   TestBackgroundTracingHelper background_tracing_helper;
   TestTraceReceiverHelper trace_receiver_helper;