Added FloatingAppBarScrollingViewBehavior

-Added FloatingAppBarScrollingViewBehavior for search bar. It can be scolling,
 transparent and overlapped the scrolling child view.
-Exchanged the position of NestedScrollView and AppBarLayout in
 settings_homepage_container.xml.
-Set the app bar height.

Change-Id: I6ef4c9001a1f893292fcbc825a0a9f2069b7286b
Fixes: 118886724
Test: robotest

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

@@ -0,0 +1,61 @@
+/*
+ * 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.widget;
+
+import android.content.Context;
+import android.graphics.Color;
+import android.util.AttributeSet;
+import android.view.View;
+
+import androidx.annotation.VisibleForTesting;
+import androidx.coordinatorlayout.widget.CoordinatorLayout;
+
+import com.google.android.material.appbar.AppBarLayout;
+
+/**
+ * This scrolling view behavior will set the background of the {@link AppBarLayout} as
+ * transparent and without the elevation. Also make header overlapped the scrolling child view.
+ */
+public class FloatingAppBarScrollingViewBehavior extends AppBarLayout.ScrollingViewBehavior {
+    private boolean initialized;
+
+    public FloatingAppBarScrollingViewBehavior(Context context, AttributeSet attrs) {
+        super(context, attrs);
+    }
+
+    @Override
+    public boolean onDependentViewChanged(CoordinatorLayout parent, View child, View dependency) {
+        boolean changed = super.onDependentViewChanged(parent, child, dependency);
+        if (!initialized && dependency instanceof AppBarLayout) {
+            initialized = true;
+            AppBarLayout appBarLayout = (AppBarLayout) dependency;
+            setAppBarLayoutTransparent(appBarLayout);
+        }
+        return changed;
+    }
+
+    @VisibleForTesting
+    void setAppBarLayoutTransparent(AppBarLayout appBarLayout) {
+        appBarLayout.setBackgroundColor(Color.TRANSPARENT);
+        appBarLayout.setTargetElevation(0);
+    }
+
+    @Override
+    protected boolean shouldHeaderOverlapScrollingChild() {
+        return true;
+    }
+}