Make a pref test more robust.
Make a pref test more robust.

Ignore errors when cleaning up.

shutil.rmtree() works by os.listdir() followed by rm'ing each entry.
If a file goes missing after os.listdir(), a os.remove will be attempted for it resulting in an exception.

In this case it might happen so (in once in a blue moon) because chrome creates temp files while downloading and cleans them up.

Review URL: http://codereview.chromium.org/3143017

git-svn-id: http://src.chromium.org/svn/trunk/src@56149 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 7686438f44b7d03c894747483b20260afc92fb8d
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