Screen Sharing: Add new UI assets.

BUG=327821
TBR=oshima

Review URL: https://codereview.chromium.org/105253003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@240205 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 240205