Disable an ExtensionWebRequestApiTest on Mac/Linux

ExtensionWebRequestApiTest.WebRequestUnloadImmediately in
renderer_side_navigation_browser_tests is flaky on Linux/Mac. This disables it.

TEST=browser_tests --disable-browser-side-navigation --gtest_filter=ExtensionWebRequestApiTest.WebRequestUnloadImmediately
TBR=battre@chromium.org

Bug: 780369
Change-Id: I61c32c1d35de888298d8344d0d367044ece64d39
Reviewed-on: https://chromium-review.googlesource.com/748661
Commit-Queue: Makoto Shimazu <shimazu@chromium.org>
Reviewed-by: Makoto Shimazu <shimazu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#513073}

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

@@ -304,8 +304,14 @@ IN_PROC_BROWSER_TEST_F(ExtensionWebRequestApiTest,
 
 // Test that the webRequest events are dispatched with the expected details when
 // a frame or tab is immediately removed after starting a request.
+// Flaky on Linux/Mac. See crbug.com/780369 for detail.
+#if defined(OS_MACOSX) || defined(OS_LINUX)
+#define MAYBE_WebRequestUnloadImmediately DISABLED_WebRequestUnloadImmediately
+#else
+#define MAYBE_WebRequestUnloadImmediately WebRequestUnloadImmediately
+#endif
 IN_PROC_BROWSER_TEST_F(ExtensionWebRequestApiTest,
-                       WebRequestUnloadImmediately) {
+                       MAYBE_WebRequestUnloadImmediately) {
   ASSERT_TRUE(StartEmbeddedTestServer());
   ASSERT_TRUE(RunExtensionSubtest("webrequest", "test_unload.html?5")) <<
       message_;