Mark test ExtensionWebRequestApiTest.ExtensionRequests as flaky

TBR=grunell@chromium.org
NOTRY=true

Bug: 859063
Change-Id: Iafc22ff3f54532562e53c7c0a11f1fe2e3c4c157
Reviewed-on: https://chromium-review.googlesource.com/1120157Reviewed-by: Yi Gu <yigu@chromium.org>
Commit-Queue: Yi Gu <yigu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571461}

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

@@ -694,7 +694,8 @@ IN_PROC_BROWSER_TEST_F(ExtensionWebRequestApiTest, IncognitoSplitModeReload) {
   EXPECT_TRUE(listener_incognito2.WaitUntilSatisfied());
 }
 
-IN_PROC_BROWSER_TEST_F(ExtensionWebRequestApiTest, ExtensionRequests) {
+// This test is flaky. See http://crbug.com/859063.
+IN_PROC_BROWSER_TEST_F(ExtensionWebRequestApiTest, DISABLED_ExtensionRequests) {
   ASSERT_TRUE(StartEmbeddedTestServer());
   ExtensionTestMessageListener listener_main1("web_request_status1", true);
   ExtensionTestMessageListener listener_main2("web_request_status2", true);