[Sheriff] disable failing ExtensionWebRequestApiTest on Linux

TBR=sky@chromium.org

Bug: 1015020
Change-Id: Ia71d6f25a54198b2210d706e7bfc9e8d663f0eb8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1864717
Commit-Queue: Parastoo Geranmayeh <parastoog@google.com>
Reviewed-by: Parastoo Geranmayeh <parastoog@google.com>
Cr-Commit-Position: refs/heads/master@{#706553}

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

@@ -599,8 +599,9 @@ IN_PROC_BROWSER_TEST_F(ExtensionWebRequestApiTest,
       << message_;
 }
 
-// Flaky on ChromeOS: https://crbug.com/1003661
-#if defined(OS_CHROMEOS)
+// Flaky on ChromeOS: https://crbug.com/1003661 and Linux:
+// https://crbug.com/1864717
+#if defined(OS_CHROMEOS) || defined(OS_LINUX)
 #define MAYBE_WebRequestExtraHeaders DISABLED_WebRequestExtraHeaders
 #else
 #define MAYBE_WebRequestExtraHeaders WebRequestExtraHeaders