[NaCl SDK AppEngine] More tweaks to the Bullet fullscreen demo.

This hides more information by default, but allows you to click a "more
info..." button to display info about Bullet and Native Client, and let you
change the scene.

BUG=none
TBR=sbc@chromium.org

Review URL: https://codereview.chromium.org/175813003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252716 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252716