Updated release notes. (Ported changes from DevSite.)

BUG=

Temporary staged doc: http://ypd-ubiq182.dls.corp.google.com:8009/sdk/release-notes.html

R=binji@chromium.org

Review URL: https://codereview.chromium.org/129793006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243975 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 243975