Add new sample code for writing a ViewGroup.

 * <a href="{@docRoot}guide/topics/ui/declaring-layout.html">XML Layouts</a> developer

 * guide.</p></div>

 *

 * <p>Here is a complete implementation of a custom ViewGroup that implements

 * a simple {@link android.widget.FrameLayout} along with the ability to stack

 * children in left and right gutters.</p>

 *

 * {@sample development/samples/ApiDemos/src/com/example/android/apis/view/CustomLayout.java

 *      Complete}

 *

 * <p>If you are implementing XML layout attributes as shown in the example, this is the

 * corresponding definition for them that would go in <code>res/values/attrs.xml</code>:</p>

 *

 * {@sample development/samples/ApiDemos/res/values/attrs.xml CustomLayout}

 *

 * <p>Finally the layout manager can be used in an XML layout like so:</p>

 *

 * {@sample development/samples/ApiDemos/res/layout/custom_layout.xml Complete}

 *

 * @attr ref android.R.styleable#ViewGroup_clipChildren

 * @attr ref android.R.styleable#ViewGroup_clipToPadding

 * @attr ref android.R.styleable#ViewGroup_layoutAnimation