Fix pngencoder mac perf errors - the previous code was never actually doing an input.empty() check.
Fix pngencoder mac perf errors - the previous code was never actually doing an input.empty() check.

BUG=none
TEST=none
TBR=nick

Review URL: http://codereview.chromium.org/118343

git-svn-id: http://src.chromium.org/svn/trunk/src@17801 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 142937616c37b76eb578a69e852b5e305085d430
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser