chromeos: disables test as it fails

This test enables tablet mode, but it enables tablet mode in such a way
that MultiUserWindowManager doesn't see (and process) the change. When
the test is updated to correctly notify MultiUserWindowManager the test then
fails. I think this may indicate a regression from recent changes and needs
to be investigated.

I came across this while doing some refactoring to MultiUserWindowManager.

I've updated the test to ensure MultiUserWindowManager is called correctly
and disabled it.

BUG=756085,903427
TEST=none

Change-Id: I7b6ead448ba8d942516e42d9ef5ee745a547cc2c
Reviewed-on: https://chromium-review.googlesource.com/c/1327159Reviewed-by: Jonathan Ross <jonross@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606567}

chrome/browser/ui/ash/multi_user/multi_user_window_manager_chromeos_unittest.cc

@@ -818,7 +818,9 @@ TEST_F(MultiUserWindowManagerChromeOSTest, PreserveInitialVisibility) {
 
 // Test that in case of an activated tablet mode, windows from other users get
 // maximized after a user switch.
-TEST_F(MultiUserWindowManagerChromeOSTest, TabletModeInteraction) {
+// TODO(sammiequon): disabled as expectations aren't correct with
+// addition of call to OnTabletModeToggled(). https://crbug.com/903427
+TEST_F(MultiUserWindowManagerChromeOSTest, DISABLED_TabletModeInteraction) {
   SetUpForThisManyWindows(2);
 
   const AccountId account_id_A(AccountId::FromUserEmail("A"));
@@ -831,9 +833,7 @@ TEST_F(MultiUserWindowManagerChromeOSTest, TabletModeInteraction) {
   EXPECT_FALSE(wm::GetWindowState(window(1))->IsMaximized());
 
   Shell::Get()->tablet_mode_controller()->EnableTabletModeWindowManager(true);
-  TabletModeWindowManager* manager =
-      TabletModeControllerTestApi().tablet_mode_window_manager();
-  ASSERT_TRUE(manager);
+  multi_user_window_manager()->OnTabletModeToggled(true);
 
   EXPECT_TRUE(wm::GetWindowState(window(0))->IsMaximized());
   EXPECT_FALSE(wm::GetWindowState(window(1))->IsMaximized());