GitLab

- Move NativeWidgetView to its own file.
- Enhances the example to contain a button.

http://crbug.com/83663
TEST=none
Review URL: http://codereview.chromium.org/7065042

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@86527 0039d316-1c4b-4281-b951-d872f2087c98