Deflake InvalidationPreferencesTest

These tests are based on SharedPreferences, which previously weren't
reset between tests, causing the tests to start with incorrect
assumptions. This CL adds a setUp() that clears the preferences, and
removes the FlakyTest annotations.

Bug: 905233
Change-Id: Ib66b506811ae38335605498d9eeef9be89d9ef08
Reviewed-on: https://chromium-review.googlesource.com/c/1340817Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Commit-Queue: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609277}

components/sync/android/javatests/src/org/chromium/components/sync/notifier/InvalidationPreferencesTest.java

@@ -10,14 +10,15 @@ import android.support.test.filters.SmallTest;
 import com.google.ipc.invalidation.external.client.types.ObjectId;
 
 import org.junit.Assert;
+import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 
 import org.chromium.base.ApiCompatibilityUtils;
 import org.chromium.base.CollectionUtil;
+import org.chromium.base.ContextUtils;
 import org.chromium.base.test.BaseJUnit4ClassRunner;
 import org.chromium.base.test.util.Feature;
-import org.chromium.base.test.util.FlakyTest;
 import org.chromium.base.test.util.RetryOnFailure;
 
 import java.util.Arrays;
@@ -31,8 +32,13 @@ import java.util.Set;
 @RunWith(BaseJUnit4ClassRunner.class)
 @RetryOnFailure
 public class InvalidationPreferencesTest {
+    @Before
+    public void setUp() {
+        // Make sure the SharedPreferences start out empty.
+        ContextUtils.getAppSharedPreferences().edit().clear().apply();
+    }
+
     @Test
-    @FlakyTest(message = "https://crbug.com/905233")
     @SmallTest
     @Feature({"Sync"})
     public void testReadMissingData() {
@@ -47,7 +53,6 @@ public class InvalidationPreferencesTest {
     }
 
     @Test
-    @FlakyTest(message = "https://crbug.com/905233")
     @SmallTest
     @Feature({"Sync"})
     public void testReadWriteAndReadData() {