Add UiBlocker for DashboardFragment

If DashboardFragment detects blocker controllers, it won't display
until:
1. All blocking controllers finish bg works.
2. Timeout

This CL adds UiBlockerController to control this behavior and
BlockingSlicePreferenceController as an example.

Bug: 120803703
Test: atest SettingsUnitTests
Change-Id: I66fc194776d46ee49b3ec7685f3167834e673ba2

tests/unit/src/com/android/settings/dashboard/UiBlockerControllerTest.java

@@ -0,0 +1,69 @@
+/*
+ * Copyright (C) 2018 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.settings.dashboard;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import android.app.Instrumentation;
+
+import androidx.test.InstrumentationRegistry;
+import androidx.test.filters.MediumTest;
+import androidx.test.runner.AndroidJUnit4;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import java.util.Arrays;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+
+@RunWith(AndroidJUnit4.class)
+@MediumTest
+public class UiBlockerControllerTest {
+    private static final long TIMEOUT = 600;
+    private static final String KEY_1 = "key1";
+    private static final String KEY_2 = "key2";
+
+    private Instrumentation mInstrumentation;
+    private UiBlockerController mSyncableController;
+
+    @Before
+    public void setUp() throws Exception {
+        mInstrumentation = InstrumentationRegistry.getInstrumentation();
+
+        mSyncableController = new UiBlockerController(Arrays.asList(KEY_1, KEY_2));
+    }
+
+    @Test
+    public void start_isSyncedReturnFalseUntilAllWorkDone() throws InterruptedException {
+        final CountDownLatch latch = new CountDownLatch(1);
+        mSyncableController.start(() -> latch.countDown());
+
+        // Return false at first
+        assertThat(mSyncableController.isBlockerFinished()).isFalse();
+
+        // Return false if only one job is done
+        mSyncableController.countDown(KEY_1);
+        assertThat(mSyncableController.isBlockerFinished()).isFalse();
+
+        // Return true if all jobs done
+        mSyncableController.countDown(KEY_2);
+        assertThat(latch.await(TIMEOUT, TimeUnit.MILLISECONDS)).isTrue();
+        assertThat(mSyncableController.isBlockerFinished()).isTrue();
+    }
+}