title: Crosswalk's XWalkView (an alternative to Webview) not working with AppBarLayout + CoordinatorLayout
body: <p>I'm trying to achieve the scrolling <code>Toolbar</code> technique (hiding <code>Toolbar</code> when scrolling down in a sibling child view) using <code>CoordinatorLayout</code> and <code>AppBarLayout</code>.</p>
  
  <p>I'm using <a href="https://crosswalk-project.org/">Crosswalk</a>'s <a href="https://crosswalk-project.org/apis/embeddingapidocs_v5/index.html">XWalkView</a> (it's a view which functions like WebView).  </p>
  
  <p>When using regular <a href="http://developer.android.com/reference/android/webkit/WebView.html">WebView</a> (inside a <code>NestedScrollView</code>) I can achieve the wanted effect:</p>
  
  <pre><code>&lt;android.support.design.widget.CoordinatorLayout
      xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:app="http://schemas.android.com/apk/res-auto"
      android:layout_width="match_parent"
      android:layout_height="match_parent"&gt;
  
      &lt;android.support.design.widget.AppBarLayout
          android:id="@+id/app_bar_layout"
          android:layout_width="match_parent"
          android:layout_height="wrap_content"&gt;
  
          &lt;android.support.v7.widget.Toolbar
              android:id="@+id/toolbar"
              android:layout_width="match_parent"
              android:layout_height="?attr/actionBarSize"
              app:layout_scrollFlags="scroll|enterAlways" /&gt;
  
      &lt;/android.support.design.widget.AppBarLayout&gt;
  
      &lt;android.support.v4.widget.NestedScrollView
          app:layout_behavior="@string/appbar_scrolling_view_behavior"
          android:layout_width="match_parent"
          android:layout_height="match_parent"&gt;
  
          &lt;WebView
              android:id="@+id/webViewOrig"
              android:layout_width="match_parent"
              android:layout_height="match_parent"/&gt;
  
      &lt;/android.support.v4.widget.NestedScrollView&gt;
  &lt;/android.support.design.widget.CoordinatorLayout&gt;
  </code></pre>
  
  <p>However when using the <code>XWalkView</code> in the same way, I can't get it to work.
  After using the following XML layout:</p>
  
  <pre><code>&lt;android.support.v4.widget.NestedScrollView
          android:id="@+id/scrollView"
          android:layout_width="match_parent"
          android:layout_height="match_parent"
          android:fillViewport = "true"
          app:layout_behavior="@string/appbar_scrolling_view_behavior"&gt;
  
          &lt;org.xwalk.core.XWalkView
              android:id="@+id/webViewCross"
              android:layout_width="match_parent"
              android:layout_height="match_parent"/&gt;
  &lt;/android.support.v4.widget.NestedScrollView&gt;
  </code></pre>
  
  <p>the view doesn't even appear.</p>
  
  <p>When removing the following line</p>
  
  <pre><code>app:layout_behavior="@string/appbar_scrolling_view_behavior"
  </code></pre>
  
  <p>the <code>XWalkView</code> is at least displayed but on the whole screen and on top of the Toolbar.</p>
  
  <p>What should I do to make it work? Since it's an open-source I should be able to make it work... I suspect it's either subclass <code>XWalkView</code> and implement some interface (<code>NestedScrollingChild</code>?) or creating a custom behaviour by subclassing <code>CoordinatorLayout.Behavior</code> or <code>AppBarLayout.ScrollingViewBehavior</code>.</p>
  
  <p>Any ideas?</p>
  
  <p>BTW <code>XWalkView</code> is using internally either <a href="http://developer.android.com/reference/android/view/SurfaceView.html">SurfaceView</a> or <a href="http://developer.android.com/reference/android/view/TextureView.html">TextureView</a> to render the web content.</p>