Show shadow when entity header starts scrolling.

- Add a controller to manage add/remove onScrollChangedListener to
  recyclerviews.
- When recyclerview on each screen is scrolled to top, set actionbar
  elevation to 0, otherwise set it to non-zero.
- When screen is moved to background, detach the listener.
- Use the controller in entity header.

Change-Id: Iecf194d885098c98c392810f62893ae9189f3936
Fix: 37670670
Test: make RunSettingsRoboTests

tests/robotests/src/com/android/settings/widget/ActionBarShadowControllerTest.java

@@ -0,0 +1,89 @@
+/*
+ * Copyright (C) 2017 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.widget;
+
+
+import android.app.ActionBar;
+import android.app.Activity;
+import android.support.v7.widget.RecyclerView;
+
+import com.android.settings.SettingsRobolectricTestRunner;
+import com.android.settings.TestConfig;
+import com.android.settingslib.core.lifecycle.Lifecycle;
+import com.android.settingslib.core.lifecycle.LifecycleObserver;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+import org.robolectric.annotation.Config;
+import org.robolectric.util.ReflectionHelpers;
+
+import java.util.List;
+
+import static com.google.common.truth.Truth.assertThat;
+import static org.mockito.Matchers.any;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+@RunWith(SettingsRobolectricTestRunner.class)
+@Config(manifest = TestConfig.MANIFEST_PATH, sdk = TestConfig.SDK_VERSION)
+public class ActionBarShadowControllerTest {
+
+    @Mock
+    private RecyclerView mRecyclerView;
+    @Mock
+    private Activity mActivity;
+    @Mock
+    private ActionBar mActionBar;
+    private Lifecycle mLifecycle;
+
+    @Before
+    public void setUp() {
+        MockitoAnnotations.initMocks(this);
+        when(mActivity.getActionBar()).thenReturn(mActionBar);
+        mLifecycle = new Lifecycle();
+    }
+
+    @Test
+    public void attachToRecyclerView_shouldAddScrollWatcherAndUpdateActionBar() {
+        when(mRecyclerView.canScrollVertically(-1)).thenReturn(false);
+
+        ActionBarShadowController.attachToRecyclerView(mActivity, mLifecycle, mRecyclerView);
+
+        verify(mActionBar).setElevation(0);
+    }
+
+
+    @Test
+    public void attachToRecyclerView_lifecycleChange_shouldAttachDetach() {
+        ActionBarShadowController.attachToRecyclerView(mActivity, mLifecycle, mRecyclerView);
+
+        List<LifecycleObserver> observers = ReflectionHelpers.getField(mLifecycle, "mObservers");
+        assertThat(observers).hasSize(1);
+        verify(mRecyclerView).addOnScrollListener(any());
+
+        mLifecycle.onStop();
+        verify(mRecyclerView).removeOnScrollListener(any());
+
+        mLifecycle.onStart();
+        verify(mRecyclerView, times(2)).addOnScrollListener(any());
+    }
+
+}