linux: properly handle pixbuf refcount
linux: properly handle pixbuf refcount

gfx::GdkPixbufFromSkBitmap() returns an image with a refcount of 1.
Fixes heapcheck error seen on buildbots.

Review URL: http://codereview.chromium.org/1578012

git-svn-id: http://src.chromium.org/svn/trunk/src@43728 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 53eadeae80c9443ba2723653fb42f999dd5c7254
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