Disable NetworkPortalDetectorImplBrowserTest.InSessionDetection.

This test has been experiencing flaky timeouts.

BUG=423094
TBR=ygorshenin@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/648383002

Cr-Commit-Position: refs/heads/master@{#299366}

chrome/browser/chromeos/net/network_portal_detector_impl_browsertest.cc

@@ -154,8 +154,9 @@ IN_PROC_BROWSER_TEST_F(NetworkPortalDetectorImplBrowserTest,
   ASSERT_EQ(PortalDetectorStrategy::STRATEGY_ID_LOGIN_SCREEN, strategy()->Id());
 }
 
+// Disabled for flaky timeouts.  http://crbug.com/423094
 IN_PROC_BROWSER_TEST_F(NetworkPortalDetectorImplBrowserTest,
-                       InSessionDetection) {
+                       DISABLED_InSessionDetection) {
   typedef NetworkPortalNotificationController Controller;
 
   TestObserver observer;