Scheme of content utils should be compared in an ASCII case-insensitive manner

Scheme has been compared in case-sensitive manner. However, according to spec, scheme must be compared in an ASCII case-insensitive manner by user agents.

Merge from WebKit : http://trac.webkit.org/changeset/169670

BUG=none

Review URL: https://codereview.chromium.org/323493003

git-svn-id: svn://svn.chromium.org/blink/trunk@175771 bbb929c8-8fbe-4397-9dbb-9b2b20218538