Move EME key system knowledge from content/ to chrome/.
Most of the knowledge about specific key systems is moved from
content/renderer/media/crypto/key_systems_info.cc to
chrome/renderer/media/chrome_key_systems.cc.
content/renderer/media/crypto/key_systems_unittest.cc is modified to test the
infrastructure rather than specific key systems, which are now tested in
chrome/browser/media/encrypted_media_istypesupported_browsertest.cc (r222647).
BUG=224793
Review URL: https://chromiumcodereview.appspot.com/
23452025
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@223132 0039d316-1c4b-4281-b951-d872f2087c98