Revise AudioWorkletNode IDL (AudioWorkletProcessorState, onprocessorerror)

Spec PR: https://github.com/WebAudio/web-audio-api/pull/1509

1. Remove AudioWorkletProcessorState from the implementation.
2. Add `onprocessorerror` to AudioWorkletNode IDL.
3. Modify the existing test for AudioWorkletProcessorState
   to test onprocessorerror handler.

Bug: 816542
Test: http/tests/webaudio/audio-worklet/audio-worklet-node-onerror.html
Change-Id: I96280c7dbed5cdf2d608633e4ddb9c94e9b4f6e7
Reviewed-on: https://chromium-review.googlesource.com/937986
Reviewed-by: Raymond Toy <rtoy@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Hongchan Choi <hongchan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#539699}
13 files changed