Add more sync tests to investigate flakiness

The purpose of the two new tests is to verify whether the test fixture
itself has flakiness issues, since most tests in the suite experience
occasional flakes, see
https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=chrome_sync_shell_test_apk&tests=SyncCustomizationFragmentTest

Bug: 879246
Change-Id: I616f075f56c91c19642b06c80a5af1f47653026b
Reviewed-on: https://chromium-review.googlesource.com/1254203Reviewed-by: Jan Krcal <jkrcal@chromium.org>
Commit-Queue: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595449}

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

@@ -118,6 +118,29 @@ public class SyncCustomizationFragmentTest {
         ThreadUtils.runOnUiThreadBlocking(() -> ProfileSyncService.resetForTests());
     }
 
+    /**
+     * Minimal test fixture to debug flakiness in the actual tests.
+     * TODO(crbug.com/879246): Remove after investigation.
+     */
+    @Test
+    @SmallTest
+    @Feature({"Sync"})
+    public void testSetupOnly() {
+        mSyncTestRule.setUpTestAccountAndSignIn();
+    }
+
+    /**
+     * Minimal test fixture to debug flakiness in the actual tests.
+     * TODO(crbug.com/879246): Remove after investigation.
+     */
+    @Test
+    @SmallTest
+    @Feature({"Sync"})
+    public void testSetupAndWaitForSyncActive() {
+        mSyncTestRule.setUpTestAccountAndSignIn();
+        SyncTestUtil.waitForSyncActive();
+    }
+
     @Test
     @SmallTest
     @Feature({"Sync"})