Made AudioNode an EventTarget
    
According to the latest draft of the WebAudio
Spec, AudioNode should be an EventTarget.

BUG=230890

Review URL: https://chromiumcodereview.appspot.com/14028011

git-svn-id: svn://svn.chromium.org/blink/trunk@150825 bbb929c8-8fbe-4397-9dbb-9b2b20218538
9 files changed