Add a test to verify lifecycle events are triggered

- Added a footer in feature flags, displaying "Experimental" during
  onStart.
- Ui test to verify the text shows correctly.

Change-Id: Ibf4f79cb3c12e460384e83201a16005a18d6437d
Fixes: 78887450
Test: atest

src/com/android/settings/development/featureflags/FeatureFlagFooterPreferenceController.java

@@ -0,0 +1,50 @@
+/*
+ * 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.development.featureflags;
+
+import android.content.Context;
+
+import com.android.settings.R;
+import com.android.settings.core.BasePreferenceController;
+import com.android.settingslib.core.lifecycle.LifecycleObserver;
+import com.android.settingslib.core.lifecycle.events.OnStart;
+import com.android.settingslib.widget.FooterPreferenceMixin;
+
+public class FeatureFlagFooterPreferenceController extends BasePreferenceController
+        implements LifecycleObserver, OnStart {
+
+    private FooterPreferenceMixin mFooterMixin;
+
+    public FeatureFlagFooterPreferenceController(Context context) {
+        super(context, "feature_flag_footer_pref");
+    }
+
+    public void setFooterMixin(FooterPreferenceMixin mixin) {
+        mFooterMixin = mixin;
+    }
+
+    @Override
+    public int getAvailabilityStatus() {
+        return AVAILABLE;
+    }
+
+    @Override
+    public void onStart() {
+        mFooterMixin.createFooterPreference()
+                .setTitle(R.string.experimental_category_title);
+    }
+}