Disable ExtensionCheckupTest.NoUserInstalledExtensions on Linux

Because it's flaky.

BUG=1163917

Change-Id: I18a3f815bb3111051500a2048bdbb9a9ac191979
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2625940
Auto-Submit: Mark Pearson <mpearson@chromium.org>
Commit-Queue: Finnur Thorarinsson <finnur@chromium.org>
Reviewed-by: Finnur Thorarinsson <finnur@chromium.org>
Cr-Commit-Position: refs/heads/master@{#843489}

chrome/browser/extensions/extension_checkup_unittest.cc

@@ -85,7 +85,14 @@ TEST_P(ExtensionCheckupTest, NoInstalledExtensions) {
 
 // Checkup is not shown if the only extensions installed are policy
 // installed, component extensions, or installed by default.
-TEST_P(ExtensionCheckupTest, NoUserInstalledExtensions) {
+//
+// Flaky on various Linux bots.  http://crbug.com/1163917
+#if defined(OS_LINUX)
+#define MAYBE_NoUserInstalledExtensions DISABLED_NoUserInstalledExtensions
+#else
+#define MAYBE_NoUserInstalledExtensions NoUserInstalledExtensions
+#endif
+TEST_P(ExtensionCheckupTest, MAYBE_NoUserInstalledExtensions) {
   AddExemptExtensions();
   VerifyNonExperimentCheckupDisabled();
   EXPECT_FALSE(ShouldShowExperimentCheckup());