For this to be consistent, this also means that the channelCountMode cannot be "max" because the implies the channelCount is ignored.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/df2695285dbd49fc66d940ea08c71e09e9cc5583

commit df2695285dbd49fc66d940ea08c71e09e9cc5583
Author: Raymond Toy <rtoy@chromium.org>
Date: Tue Aug 15 21:43:07 2017

channelCount and channelCountMode constraints for DynamicsCompressor

For the DynamicsCompressorNode, the channelCount is constrained to be
one or two.  This implies that channelCountMode cannot be "max".
Implement these constraints.

Test updated to verify these constraints.

This makes DynamicsCompressorNode consistent with StereoPannerNode and
PannerNode which are also limited to supporting only mono and stereo
inputs.

Bug:  737142 
Test: dynamicscompressor.html
Change-Id: Iaf405d40eff2c778e61c95ef54cbba709d54c885
Reviewed-on: https://chromium-review.googlesource.com/550597
Reviewed-by: Hongchan Choi <hongchan@chromium.org>
Commit-Queue: Raymond Toy <rtoy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#494560}
[modify] https://crrev.com/df2695285dbd49fc66d940ea08c71e09e9cc5583/third_party/WebKit/LayoutTests/webaudio/constructor/dynamicscompressor.html
[modify] https://crrev.com/df2695285dbd49fc66d940ea08c71e09e9cc5583/third_party/WebKit/Source/modules/webaudio/DynamicsCompressorNode.cpp
[modify] https://crrev.com/df2695285dbd49fc66d940ea08c71e09e9cc5583/third_party/WebKit/Source/modules/webaudio/DynamicsCompressorNode.h

Patch landed.