Disable flaky ActivityLogApiTest.TriggerEvent on Linux.

It was already disabled for flakiness on Mac and Windows.

TBR=kelvinjiang@chromium.org

Bug: 299393
Change-Id: I2d888b18a24b361891cc6789ca3230c71b9308f8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1772784Reviewed-by: Darren Shen <shend@chromium.org>
Commit-Queue: Darren Shen <shend@chromium.org>
Cr-Commit-Position: refs/heads/master@{#691057}

chrome/browser/extensions/api/activity_log_private/activity_log_private_apitest.cc

@@ -57,8 +57,8 @@ class ActivityLogApiTest : public ExtensionApiTest {
   base::CommandLine saved_cmdline_;
 };
 
-#if defined(OS_WIN) || defined(OS_MACOSX)
-// TODO(crbug.com/299393): Flaky on Mac and Windows.
+#if defined(OS_WIN) || defined(OS_MACOSX) || defined(OS_LINUX)
+// TODO(crbug.com/299393): Flaky on Mac, Windows and Linux.
 #define MAYBE_TriggerEvent DISABLED_TriggerEvent
 #else
 #define MAYBE_TriggerEvent TriggerEvent