net: enable ChaCha20 based cipher suites.

Soon the patch to boost AES-GCM cipher suites when AES-NI is supported will
land. Also, Google frontend servers will be configured with an equal
preference for ChaCha20 and AES-GCM, meaning that they will respect the
client's preference between those two families of ciphers.

Thus this change enables ChaCha20. Initially these cipher suites will be used
for all HTTPS connections to Google until the equal preference is configured.
At that point they'll only be used when hardware AES-GCM support isn't enabled.

BUG=310768

Review URL: https://codereview.chromium.org/92703002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238202 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238202