[sheriff] Disable IPCMojoBootstrapTest.ReceiveEmptyMessage

It's flaky as of https://chromium-review.googlesource.com/981445

Bug: 826450
Change-Id: I44227231a3cc954afab40e02508bb9fd552c1507
TBR: rockot@chromium.org, wez@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/982536
Commit-Queue: Roger McFarlane <rogerm@chromium.org>
Reviewed-by: Roger McFarlane <rogerm@chromium.org>
Reviewed-by: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#546259}

ipc/ipc_mojo_bootstrap_unittest.cc

@@ -165,7 +165,8 @@ MULTIPROCESS_TEST_MAIN_WITH_SETUP(
   return 0;
 }
 
-TEST_F(IPCMojoBootstrapTest, ReceiveEmptyMessage) {
+// TODO(https://crbug.com/826450): Fix flakiness and re-enable.
+TEST_F(IPCMojoBootstrapTest, DISABLED_ReceiveEmptyMessage) {
   base::MessageLoop message_loop;
   Connection connection(
       IPC::MojoBootstrap::Create(