Disable ExternalProviderImplTest.BlockedExternalUserProviders on Linux.

Disabling this test to reduce jank on the bots.

TBR=domfc@chromium.org

Bug: 1023391
Change-Id: I26243bb6acba2af947357222ac1fa5664601b1e0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1908063Reviewed-by: James MacLean <wjmaclean@chromium.org>
Commit-Queue: James MacLean <wjmaclean@chromium.org>
Cr-Commit-Position: refs/heads/master@{#714232}

chrome/browser/extensions/external_provider_impl_unittest.cc

@@ -230,7 +230,13 @@ TEST_F(ExternalProviderImplTest, InAppPayments) {
       extension_misc::kInAppPaymentsSupportAppId));
 }
 
-TEST_F(ExternalProviderImplTest, BlockedExternalUserProviders) {
+// https://crbug.com/1023391
+#if defined(OS_LINUX)
+#define MAYBE_BlockedExternalUserProviders DISABLED_BlockedExternalUserProviders
+#else
+#define MAYBE_BlockedExternalUserProviders BlockedExternalUserProviders
+#endif
+TEST_F(ExternalProviderImplTest, MAYBE_BlockedExternalUserProviders) {
   OverrideExternalExtensionsPath();
   InitServiceWithExternalProviders(true);