[sheriff] Disable ManifestBrowserTest.MixedContentManifest

The test is flaky on Linux, ChromeOS and Android.

TBR=dominickn@chromium.org

Bug: 1167226
Change-Id: I98fb83da5c47fd0aed1e05045fbd2ecbf2886b3b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2633090
Commit-Queue: Fabrice de Gans-Riberi <fdegans@chromium.org>
Auto-Submit: Fabrice de Gans-Riberi <fdegans@chromium.org>
Reviewed-by: Yi Gu <yigu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#844146}

content/browser/manifest/manifest_browsertest.cc

@@ -426,7 +426,8 @@ IN_PROC_BROWSER_TEST_F(ManifestBrowserTest, CorsManifestWithAcessControls) {
 
 // If a page's manifest is in an insecure origin while the page is in a secure
 // origin, requesting the manifest should return the empty manifest.
-IN_PROC_BROWSER_TEST_F(ManifestBrowserTest, MixedContentManifest) {
+// TODO(crbug.com/1167226): Flaky test.
+IN_PROC_BROWSER_TEST_F(ManifestBrowserTest, DISABLED_MixedContentManifest) {
   ASSERT_TRUE(cors_embedded_test_server()->Start());
   std::unique_ptr<net::EmbeddedTestServer> https_server(
       new net::EmbeddedTestServer(net::EmbeddedTestServer::TYPE_HTTPS));