title: (Design Support Library) CollapsingToolbarLayout -- Toolbar not getting pinned on collapse
body: <p>I'm having trouble integrating the Design Support Library into my application. For some reason, the toolbar collapses with the CollapsingToolbarLayout, and does not leave it pinned like in the Cheesesquare example by Chris Banes.
  <a href="https://github.com/chrisbanes/cheesesquare" rel="noreferrer">https://github.com/chrisbanes/cheesesquare</a></p>
  
  <p>I didn't do anything different to my layout. In fact, I replaced my styles with his, and dropped in his layout. I wonder if using Toolbar, instead of android.support.v7.widget.Toolbar is causing this.</p>
  
  <p>Here is the problem.</p>
  
  <p><img src="https://i.stack.imgur.com/zI8Vz.gif" alt="The Problem"></p>
  
  <p>Here is my XML of the AppBar section.</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:id="@+id/main_content"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:fitsSystemWindows="true"&gt;
  
  
      &lt;android.support.design.widget.AppBarLayout
          android:id="@+id/appbar"
          android:layout_width="match_parent"
          android:layout_height="@dimen/detail_backdrop_height"
          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"
              android:fitsSystemWindows="true"
              app:contentScrim="?attr/colorPrimary"
              app:expandedTitleMarginStart="48dp"
              app:expandedTitleMarginEnd="64dp"&gt;
  
              &lt;ImageView
                  android:id="@+id/backdrop"
                  android:layout_width="match_parent"
                  android:layout_height="match_parent"
                  android:fitsSystemWindows="true"
                  app:layout_collapseMode="parallax" /&gt;
  
              &lt;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.design.widget.CoordinatorLayout&gt;
  </code></pre>