title: ViewPager.PageTransformer with a drop shadow
body: <p>I have a stack of fragments in a ViewPager, with a custom PageTransformer defined as below.</p>
  
  <pre><code>mPager.setPageTransformer(true, new ViewPager.PageTransformer() {
      @Override
      public void transformPage(View page, float position) {
          page.setTranslationX(page.getWidth() * -position);
      }
  }); 
  </code></pre>
  
  <p>How can I draw a shadow for the leaving fragment ?
  Long story short I'm looking for something as in Play Book, no curl effects needed, just the shadow of the element on the top of the stack, preferably API 18 compliant</p>
  
  <p>Thank you</p>