Support IDNA 2008 with UTS46.

UTS 46 provides a migration path from IDNA 2003 to IDNA 2008.

1. Use the up-to-date Unicode data; new characters were
added and some case-folding/mapping have changed since Unicode 3.2 on which
IDNA 2003 is based.
2. Define a case folding/mapping as is the case with IDNA 2003.
3. Use transitional mechanism for 4 deviant characters : German sharp-S,
Greek final-sigma, ZWJ and ZWNJ. That is, the former two are mapped to
'ss' and regular sigma and the latter two are dropped. All the major
browsers do this at the moment so allowing them does not do any good.
We'll review this later as the consensus builds among browser vendors
and registrars. We can also consider handling them separately. For instance,
ZWJ/ZWNJ can be allowed with ContextJ rules, which requires a minor change
in ICU's UTS 46 implementation.
4. Symbol and punctuations continue to be allowed.

We also do the following:

1. Continue to "violate" STD3 rules about non-LDH (Letter, digits and
hyphens) by allowing non-LDH's. That is no change from the current
implementation.
2. Do not allow unassigned code points any more. With an up-to-date
Unicode data, this does not make much difference. And the chance of
new characters not yet reflected in our Unicode data popping up in
a domain name is extremely low.
3. Continue to use CHECK_BIDI. The Bidi rule in IDNA 2008 is more
permissive than in IDNA 2003.

References:
1. http://unicode.org/reports/tr46/ and references therein
   to IDNA 2003 and 2008 RFCs.
2. What IE 10 does : http://goo.gl/3XBhqw
3. Mozilla bug :  https://bugzilla.mozilla.org/show_bug.cgi?id=479520

BUG=61328
TEST=url_unittests (URLCanonTest.Host), net_unittests (NetUtilTest.IDNToU*),
unittests (X509CertificateModelTest.*)

R=brettw@chromium.org, pkasting@chromium.org, rsleevi@chromium.org, thakis@chromium.org

Review URL: https://codereview.chromium.org/23642003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225878 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225878