Disable o.c.c.b.sync.SyncTest#testStopAndClear

Reason: flaky

TBR=zea@chromium.org

Bug: 776251
Change-Id: I82c27e2a9586fb9560a03ed9d2f823020c7a55e0
Reviewed-on: https://chromium-review.googlesource.com/728220Reviewed-by: Egor Pasko <pasko@chromium.org>
Commit-Queue: Egor Pasko <pasko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#510074}

chrome/android/sync_shell/javatests/src/org/chromium/chrome/browser/sync/SyncTest.java

@@ -85,9 +85,12 @@ public class SyncTest {
         SyncTestUtil.waitForSyncActive();
     }
 
+    /*
+     * @LargeTest
+     * @Feature({"Sync"})
+     */
     @Test
-    @LargeTest
-    @Feature({"Sync"})
+    @DisabledTest(message = "crbug.com/776251")
     public void testStopAndClear() {
         mSyncTestRule.setUpTestAccountAndSignIn();
         CriteriaHelper.pollUiThread(