Reenable image_decoding

BUG=323015
TBR=tonyg
NOTRY=True

Review URL: https://codereview.chromium.org/149773002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247787 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247787