title: Android data binding is not working with <merge> attributes
body: <p>I'm trying to use databinding with custom views (a possible usage George Mount showed <a href="https://stackoverflow.com/a/34817565/2938966">here</a>).</p>
  
  <p>One can't imagine building compound views without <code>&lt;merge&gt;</code> tag. However, in this situation databinding fails:</p>
  
  <p><code>MyCompoundView</code> class: </p>
  
  <pre><code>public class MyCompoundView extends RelativeLayout {
  
  MyCompoundViewBinding binding;
  
  public MyCompoundView (Context context, AttributeSet attrs) {
      super(context, attrs);
      init(context);
  }
  
  private void init(Context context){
      LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
      binding = MyCompoundViewBinding.inflate(inflater, this, true);
  }
  </code></pre>
  
  <p><code>my_compound_view.xml</code>: by <code>app:isGone="@{!data.isViewVisible}"</code> i hoped to control the visibility of the whole compound view</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  
  &lt;layout
      xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:app="http://schemas.android.com/apk/res-auto"
      &gt;
  
      &lt;data&gt;
          &lt;variable name="data" type="com.example.MyViewModel"/&gt;
      &lt;/data&gt;
  
      &lt;merge
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          app:isGone="@{!data.isViewVisible}"&gt;
  
          &lt;ImageView
              android:id="@+id/image_image"
              android:layout_width="60dp"
              android:layout_height="60dp"
              app:imageUrl="@{data.imagePhotoUrl}"/&gt;
  
           &lt;!-- tons of other views--&gt;
  
      &lt;/merge&gt;
  
  &lt;/layout&gt;
  </code></pre>
  
  <p>The compiler errors:</p>
  
  <pre><code>Error:(13) No resource identifier found for attribute 'isGone' in package 'com.example'
  Error:(17, 21) No resource type specified (at 'isGone' with value '@{!data.isViewVisible}').
  </code></pre>
  
  <p>I have all needed <code>@BindingAdapter</code> methods. Now I inherit the view from <code>FrameLayout</code> and use <code>&lt;RelativeLayout&gt;</code> instead of <code>&lt;merge&gt;</code> - and it works. But I have extra nested layout. </p>
  
  <p><strong>Question:</strong> <code>merge</code> attrs are ignored. Is there any way to workaround that?</p>
  
  <p>Android Studio 1.5.1 stable</p>
  
  <p>Gradle plugin <code>com.android.tools.build:gradle:1.5.0</code></p>