Make canPlayType()'s keySystem argument depend on PrefixedEncryptedMedia

The argument is no longer marked as optional, as that would make it
ambiguous with the single-argument canPlayType().

BUG=452098

Review URL: https://codereview.chromium.org/876863006

git-svn-id: svn://svn.chromium.org/blink/trunk@189099 bbb929c8-8fbe-4397-9dbb-9b2b20218538
2 files changed
tree: 28026d0e52c3ba898e76a92ca69494d3a52f0065
  1. third_party/