Add lifecycle observers for future mixin structures.

- Converted VisibilityLoggerMixin into a LifecyclerObservable so we
  don't have to call logger.onResume/onPause manually in most fragments.
- Observable will be useful when we provide logics across all
  fragment/activity, eg log lifecycle event latencies.
- Also added new tests for lifecycle component.

Bug: 30681529
Test: RunSettingsRoboTests

Change-Id: Ida39300aeb42f71b2e0bbfaebd0c51dc468cb5e8

tests/robotests/src/com/android/settings/utils/ThreadUtilsTest.java

@@ -0,0 +1,61 @@
+/*
+ * Copyright (C) 2016 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.utils;
+
+
+import com.android.settings.TestConfig;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.robolectric.RobolectricTestRunner;
+import org.robolectric.annotation.Config;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+
+@RunWith(RobolectricTestRunner.class)
+@Config(manifest = TestConfig.MANIFEST_PATH, sdk = TestConfig.SDK_VERSION)
+public class ThreadUtilsTest {
+
+    @Test
+    public void testMainThread() throws InterruptedException {
+        assertTrue(ThreadUtils.isMainThread());
+        Thread background = new Thread(new Runnable() {
+            public void run() {
+                assertFalse(ThreadUtils.isMainThread());
+            }
+        });
+        background.start();
+        background.join();
+    }
+
+    @Test
+    public void testEnsureMainThread() throws InterruptedException {
+        ThreadUtils.ensureMainThread();
+        Thread background = new Thread(new Runnable() {
+            public void run() {
+                try {
+                    ThreadUtils.ensureMainThread();
+                    fail("Should not pass ensureMainThread in a background thread");
+                } catch (RuntimeException e) {
+                }
+            }
+        });
+        background.start();
+        background.join();
+    }
+}