Fix a DCHECK we hit when a mime type isn't ASCII.
Fix a DCHECK we hit when a mime type isn't ASCII.

I have a layout test for this, but Tony says I should send it upstream
so that will be a separate commit.

BUG=17958

Review URL: http://codereview.chromium.org/160363

git-svn-id: dd90618784b6a4b323ea0c23a071cb1c9e6f2ac7@22279 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser