Add HiDPI webstore icons. Use them on NTP and extensions domui.

BUG=134372
TEST=none
TBR=sky

Review URL: https://chromiumcodereview.appspot.com/10704053

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@145332 0039d316-1c4b-4281-b951-d872f2087c98
9 files changed