Don't draw divider under headers

Create SettingsDividerItemDecoration which reads PreferenceViewHolder
isDividerAllowedAbove/Below so that will be taken into account as
well as other ViewHolders which implements DividedViewHolder.

Bug: 28445348
Change-Id: I73e298f2ca1688b135e533a8d3ef5f5c154963f7

src/com/android/settings/utils/SettingsDividerItemDecoration.java

@@ -0,0 +1,46 @@
+/*
+ * 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 android.content.Context;
+import android.support.v7.preference.PreferenceViewHolder;
+import android.support.v7.widget.RecyclerView;
+
+import com.android.setupwizardlib.DividerItemDecoration;
+
+public class SettingsDividerItemDecoration extends DividerItemDecoration {
+
+    public SettingsDividerItemDecoration(Context context) {
+        super(context);
+    }
+
+    @Override
+    protected boolean isDividerAllowedAbove(RecyclerView.ViewHolder viewHolder) {
+        if (viewHolder instanceof PreferenceViewHolder) {
+            return ((PreferenceViewHolder) viewHolder).isDividerAllowedAbove();
+        }
+        return super.isDividerAllowedAbove(viewHolder);
+    }
+
+    @Override
+    protected boolean isDividerAllowedBelow(RecyclerView.ViewHolder viewHolder) {
+        if (viewHolder instanceof PreferenceViewHolder) {
+            return ((PreferenceViewHolder) viewHolder).isDividerAllowedBelow();
+        }
+        return super.isDividerAllowedBelow(viewHolder);
+    }
+}