DynamicsCompressor.channelCountMode is 'clamped-max'

As mentioned in the spec (https://webaudio.github.io/web-audio-api/#dynamicscompressornode),
the channelCountMode defaults to "clamped-max", not "max".  Make it so.

Bug: 835946
Test: webaudio/constructor/dynamicscompressor.html
Change-Id: I8aee3336a89ff5662ecbe7afee1793cb94184169
Reviewed-on: https://chromium-review.googlesource.com/1024791
Commit-Queue: Raymond Toy <rtoy@chromium.org>
Reviewed-by: Hongchan Choi <hongchan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553252}

third_party/WebKit/LayoutTests/webaudio/constructor/dynamicscompressor.html

@@ -34,7 +34,7 @@
               numberOfInputs: 1,
               numberOfOutputs: 1,
               channelCount: 2,
-              channelCountMode: 'max',
+              channelCountMode: 'clamped-max',
               channelInterpretation: 'speakers'
             });
 
@@ -160,7 +160,7 @@
 
         should(node.channelCount, 'node1.channelCount').beEqualTo(2);
         should(node.channelCountMode, 'node1.channelCountMode')
-            .beEqualTo('max');
+            .beEqualTo('clamped-max');
         should(node.channelInterpretation, 'node1.channelInterpretation')
             .beEqualTo('speakers');
 

third_party/blink/renderer/modules/webaudio/dynamics_compressor_node.cc

@@ -54,6 +54,9 @@ DynamicsCompressorHandler::DynamicsCompressorHandler(
       release_(&release) {
   AddInput();
   AddOutput(defaultNumberOfOutputChannels);
+
+  SetInternalChannelCountMode(kClampedMax);
+
   Initialize();
 }