title: CollapsingToolbarLayout with a ViewPager
body: <p>I'm trying to use the CollapsingToolbarLayout to have a collapsible toolbar with a ViewPager that fades away while scrolling up but I seem to lose the ability to scroll up if the ViewPager is present.</p>
  
  <p>The ViewPager is supposed to show multiple images in the Toolbar.</p>
  
  <p>Here's the XML:</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"
      android:fitsSystemWindows="true"&gt;
  
      &lt;android.support.design.widget.AppBarLayout
          android:id="@+id/app_bar_layout"
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
          android:fitsSystemWindows="true"&gt;
  
          &lt;android.support.design.widget.CollapsingToolbarLayout
              android:id="@+id/collapsing_toolbar"
              android:layout_width="match_parent"
              android:layout_height="match_parent"
              app:layout_scrollFlags="scroll|exitUntilCollapsed"
              app:contentScrim="?attr/colorPrimary"
              android:fitsSystemWindows="true"&gt;
  
              &lt;android.support.v4.view.ViewPager
                  android:id="@+id/pager"
                  android:layout_width="match_parent"
                  android:layout_height="wrap_content"
                  app:layout_collapseMode="parallax"
                  android:fitsSystemWindows="true"&gt;
              &lt;/android.support.v4.view.ViewPager&gt;
  
              &lt;android.support.v7.widget.Toolbar
                  android:id="@+id/toolbar"
                  android:layout_width="match_parent"
                  android:layout_height="?attr/actionBarSize"
                  app:popupTheme="@style/ThemeOverlay.AppCompat.Light"
                  app:layout_collapseMode="pin" /&gt;
  
          &lt;/android.support.design.widget.CollapsingToolbarLayout&gt;
  
      &lt;/android.support.design.widget.AppBarLayout&gt;
  
      &lt;android.support.v4.widget.NestedScrollView
          android:id="@+id/scroll"
          android:layout_width="match_parent"
          android:layout_height="match_parent"
          android:clipToPadding="false"
          app:layout_behavior="@string/appbar_scrolling_view_behavior"&gt;
  
          &lt;!-- Content --&gt;
  
      &lt;/android.support.v4.widget.NestedScrollView&gt;
  
  &lt;/android.support.design.widget.CoordinatorLayout&gt;
  </code></pre>