Remove divider lines from all PreferenceFragments.

(this is partially revert of ag/I0ce486f7ac6)

- Only draw divider lines on top of PreferenceCategory and
  FooterPreference

Bug: 33601143
Test: make RunSettingsRoboTests
Change-Id: I26146dcae1603dc807e54ea431910685107be94c

src/com/android/settings/widget/PreferenceDividerDecoration.java

@@ -0,0 +1,79 @@
+/*
+ * 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.widget;
+
+import android.graphics.Canvas;
+import android.graphics.drawable.Drawable;
+import android.support.v4.view.ViewCompat;
+import android.support.v7.preference.Preference;
+import android.support.v7.preference.PreferenceCategory;
+import android.support.v7.preference.PreferenceGroupAdapter;
+import android.support.v7.widget.RecyclerView;
+import android.view.View;
+
+public class PreferenceDividerDecoration extends RecyclerView.ItemDecoration {
+
+    private Drawable mDivider;
+    private int mDividerHeight;
+
+    public void setDivider(Drawable divider) {
+        if (divider != null) {
+            mDividerHeight = divider.getIntrinsicHeight();
+        } else {
+            mDividerHeight = 0;
+        }
+        mDivider = divider;
+    }
+
+    public void setDividerHeight(int dividerHeight) {
+        mDividerHeight = dividerHeight;
+    }
+
+    @Override
+    public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
+        if (mDivider == null) {
+            return;
+        }
+        final int childCount = parent.getChildCount();
+        final int width = parent.getWidth();
+        for (int childViewIndex = 0; childViewIndex < childCount; childViewIndex++) {
+            final View view = parent.getChildAt(childViewIndex);
+            if (shouldDrawDividerAbove(view, parent)) {
+                int top = (int) ViewCompat.getY(view);
+                mDivider.setBounds(0, top, width, top + mDividerHeight);
+                mDivider.draw(c);
+            }
+        }
+    }
+
+    private boolean shouldDrawDividerAbove(View view, RecyclerView parent) {
+        final RecyclerView.Adapter adapter = parent.getAdapter();
+        if (adapter == null || !(adapter instanceof PreferenceGroupAdapter)) {
+            return false;
+        }
+        final PreferenceGroupAdapter prefAdapter = (PreferenceGroupAdapter) adapter;
+        final int adapterPosition = parent.getChildAdapterPosition(view);
+        if (adapterPosition == RecyclerView.NO_POSITION) {
+            return false;
+        }
+        final Preference pref = prefAdapter.getItem(adapterPosition);
+        if (pref instanceof PreferenceCategory) {
+            return adapterPosition != 0;
+        }
+        return pref instanceof FooterPreference;
+    }
+}