Don't try to set transparency on pixbufs that don't have any transparency channel.
Don't try to set transparency on pixbufs that don't have any transparency channel.

Also add DCHECK to make sure the assumption rowstride >= width * 4 is true.

The reason this didn't cause any crashes or graphical corruption is because the non-transparent images don't have any white in them (luckily we are not making a browser for an ipod).

BUG=16749
TEST=valgrind the browser, open find bar

Review URL: http://codereview.chromium.org/155547

git-svn-id: http://src.chromium.org/svn/trunk/src@20701 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 89e20a13eed3b41f058df9a6c9f92254f2e14866
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