Icon for installing ephemeral apps

BUG=339253
R=tapted@chromium.org
TBR=jochen@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/179993008

Patch from Thanh-Mai Diep <tmdiep@chromium.org>.

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253328 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253328