libyuv roll from 978 to 979. libyuv.gyp fix for ios sim which is intel not arm, fixing a link error.
BUG=none
TEST=try bot=ios_dbg_simulator
R=wjia@chromium.org

Review URL: https://codereview.chromium.org/152993003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249502 0039d316-1c4b-4281-b951-d872f2087c98