Web MIDI: implement WebMIDIClient to handle permissions

Implement WebMIDIClient to handle permissions and remove dependencies on
old platform APIs. This transition is needed to remove old interfaces from
platform APIs.

BUG=163795

Review URL: https://chromiumcodereview.appspot.com/18611005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@213644 0039d316-1c4b-4281-b951-d872f2087c98
14 files changed