[SiteChip] Image grids for background rendering of the site chip.

R=oshima@chromium.org
BUG=315944

Review URL: https://codereview.chromium.org/78783007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236577 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 236577