Disable flaky test PrefetchBackgroundTaskTest#testReschedule

TBR=dewittj@chromium.org,jianli@chromium.org
BUG=875433

Change-Id: Ie19eea6bc5b131884f6f25d3ba0ad1fe4b9dc9ad
Reviewed-on: https://chromium-review.googlesource.com/1180358Reviewed-by: Tien-Ren Chen <trchen@chromium.org>
Commit-Queue: Tien-Ren Chen <trchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584224}

chrome/android/javatests/src/org/chromium/chrome/browser/offlinepages/prefetch/PrefetchBackgroundTaskTest.java

@@ -236,6 +236,7 @@ public class PrefetchBackgroundTaskTest {
 
     @Test
     @SmallTest
+    @DisabledTest(message = "crbug.com/875433")
     public void testReschedule() throws Exception {
         PrefetchBackgroundTask.skipConditionCheckingForTesting();
         scheduleTask(0);