title: Change drawer icon back to back arrow
body: <p>I'm using the new <code>DrawerLayout</code> to have side navigation. I'm using the drawer icon (the 'hamburger') like this:</p>
  
  <pre><code>@Override
  protected void onStart() {
      super.onStart();
  
      mDrawerLayout = (DrawerLayout) findViewById(R.id.activity_main_drawerlayout);
      mDrawerToggle = new ActionBarDrawerToggle(
              this, 
              mDrawerLayout, 
              R.drawable.ic_navigation_drawer, 
              R.string.app_name, 
              R.string.app_name);
      mDrawerLayout.setDrawerListener(mDrawerToggle);
  
      getActionBar().setDisplayHomeAsUpEnabled(true);
      getActionBar().setHomeButtonEnabled(true);
  }
  </code></pre>
  
  <p>However, when I add a <code>Fragment</code> to the backstack, I want to display the back arrow again, so the user can navigate back to "home", and only then open the app drawer.</p>
  
  <p>How can I reset the drawer icon to the back icon?<br>
  The arrow I want:</p>
  
  <p><img src="https://i.stack.imgur.com/f9Jpw.png" alt="Navigation Drawer"></p>