Disable flaky test RedirectToAppCacheRequest on Linux

The test has been flaky (score > 1400):
https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=browser_tests%20(with%20patch)&tests=ExtensionWebRequestApiTest.RedirectToAppCacheRequest

https://analysis.chromium.org/p/chromium/flake-portal/flakes/occurrences?key=ag9zfmZpbmRpdC1mb3ItbWVyVgsSBUZsYWtlIktjaHJvbWl1bUBicm93c2VyX3Rlc3RzQEV4dGVuc2lvbldlYlJlcXVlc3RBcGlUZXN0LlJlZGlyZWN0VG9BcHBDYWNoZVJlcXVlc3QM

There are other instances on Mac but not as many as on Linux ATM.

TBR=cduvall@chromium.org
Bug: 1094834

Change-Id: I28ff7697b3cd7cbd8f81ced7f0dd4cfb4d53103f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2559005Reviewed-by: Yi Gu <yigu@chromium.org>
Commit-Queue: Yi Gu <yigu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#830761}

chrome/browser/extensions/api/web_request/web_request_apitest.cc

@@ -3030,7 +3030,14 @@ IN_PROC_BROWSER_TEST_F(ExtensionWebRequestApiTest, AppCacheRequests) {
 
 // Regression test for http://crbug.com/996940. Requests that redirected to an
 // appcache handled URL could have request ID collisions.
-IN_PROC_BROWSER_TEST_F(ExtensionWebRequestApiTest, RedirectToAppCacheRequest) {
+// This test is flaky on Linux: https://crbug.com/1094834.
+#if defined(OS_LINUX)
+#define MAYBE_RedirectToAppCacheRequest DISABLED_RedirectToAppCacheRequest
+#else
+#define MAYBE_RedirectToAppCacheRequest RedirectToAppCacheRequest
+#endif
+IN_PROC_BROWSER_TEST_F(ExtensionWebRequestApiTest,
+                       MAYBE_RedirectToAppCacheRequest) {
   // Use the embedded test server to support server-redirect, but serve
   // appcache from a fixed port using the url loader interceptor below
   // so that the appcache origin trial works.