Disable VolumeManagerTest.OnRenameEvent_Completed

Disable the test on ChromeOS due to flaky.

Tbr: petewil@chromium.org
Bug: 938755
Change-Id: I99eb58c46f53ae6cac8c2925171b7c3e838e15b8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1506119Reviewed-by: Owen Min <zmin@chromium.org>
Commit-Queue: Owen Min <zmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638217}

chrome/browser/chromeos/file_manager/volume_manager_unittest.cc

@@ -1007,7 +1007,7 @@ TEST_F(VolumeManagerTest, OnRenameEvent_StartFailed) {
   volume_manager()->RemoveObserver(&observer);
 }
 
-TEST_F(VolumeManagerTest, OnRenameEvent_Completed) {
+TEST_F(VolumeManagerTest, DISABLED_OnRenameEvent_Completed) {
   LoggingObserver observer;
   volume_manager()->AddObserver(&observer);