The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/1c9cd237a86b9e9315f2236b5ecf76fd54065eb9

commit 1c9cd237a86b9e9315f2236b5ecf76fd54065eb9
Author: Hongchan Choi <hongchan@chromium.org>
Date: Tue Jun 06 18:01:53 2017

Implement parsing parameterDescriptors() in AudioWorkletGlobalScope

According to the spec[1], this CL adds the parsing routine for
paramterDescriptors() in AudioWorkletProcessor class when the
definition is registered in AudioWorkletGlobalScope.

[1] https://webaudio.github.io/web-audio-api/#instantiation-of-AudioWorkletNode-and-AudioWorkletProcessor

Bug:  728342 
Change-Id: I79ca0aab6684cac2c9ab18d4366ec5c6d69d715b
Reviewed-on: https://chromium-review.googlesource.com/521386
Commit-Queue: Hongchan Choi <hongchan@chromium.org>
Reviewed-by: Raymond Toy <rtoy@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#477337}
[modify] https://crrev.com/1c9cd237a86b9e9315f2236b5ecf76fd54065eb9/third_party/WebKit/Source/modules/modules_idl_files.gni
[add] https://crrev.com/1c9cd237a86b9e9315f2236b5ecf76fd54065eb9/third_party/WebKit/Source/modules/webaudio/AudioParamDescriptor.idl
[modify] https://crrev.com/1c9cd237a86b9e9315f2236b5ecf76fd54065eb9/third_party/WebKit/Source/modules/webaudio/AudioWorkletGlobalScope.cpp
[modify] https://crrev.com/1c9cd237a86b9e9315f2236b5ecf76fd54065eb9/third_party/WebKit/Source/modules/webaudio/AudioWorkletGlobalScopeTest.cpp
[modify] https://crrev.com/1c9cd237a86b9e9315f2236b5ecf76fd54065eb9/third_party/WebKit/Source/modules/webaudio/AudioWorkletProcessorDefinition.cpp
[modify] https://crrev.com/1c9cd237a86b9e9315f2236b5ecf76fd54065eb9/third_party/WebKit/Source/modules/webaudio/AudioWorkletProcessorDefinition.h