Make AudioBufferSourceNode.buffer setter conforming

third_party/WebKit/LayoutTests/webaudio/AudioBufferSource/audiobuffersource-channels.html

Index: third_party/WebKit/LayoutTests/webaudio/AudioBufferSource/audiobuffersource-channels.html
diff --git a/third_party/WebKit/LayoutTests/webaudio/AudioBufferSource/audiobuffersource-channels.html b/third_party/WebKit/LayoutTests/webaudio/AudioBufferSource/audiobuffersource-channels.html
index 0e4bfb3598b7cee3d8ebc22e706a9bbe71c29acf..0ac5c66ea1a3b509e5c9c3f0959a19390dbd75bc 100644
--- a/third_party/WebKit/LayoutTests/webaudio/AudioBufferSource/audiobuffersource-channels.html
+++ b/third_party/WebKit/LayoutTests/webaudio/AudioBufferSource/audiobuffersource-channels.html
@@ -30,9 +30,39 @@
               source.buffer = 57;
             }, 'source.buffer = 57').throw('TypeError');
 
+            // It's ok to set the buffer to null.
             should(function() {
               source.buffer = null;
-            }, 'source.buffer = null').throw('TypeError');
+            }, 'source.buffer = null').notThrow();
+
+            // Set the buffer to a valid AudioBuffer
+            let buffer =
+                new AudioBuffer({length: 128, sampleRate: context.sampleRate});
+
+            should(function() {

[hongchan, 2017/07/28 18:45:32]

We prefer |()=>| over |function()|.

[Raymond Toy, 2017/07/28 19:16:55]

I was fallowing the existing code which was using function().  Let's leave it
and convert function() to ()=> later.

+              source.buffer = buffer;
+            }, 'source.buffer = buffer').notThrow();
+
+            // The buffer has been set; we can't set it again.
+            should(function() {
+              source.buffer =
+                  new AudioBuffer({length: 128, sampleRate: context.sampleRate})
+            }, 'source.buffer = new buffer').throw('InvalidStateError');
+
+            // The buffer has been set; it's ok to set it to null.
+            should(function() {
+              source.buffer = null;
+            }, 'source.buffer = null again').notThrow();
+
+            // The buffer was already set (and set to null).  Can't set it
+            // again.
+            should(function() {
+              source.buffer = buffer;
+            }, 'source.buffer = buffer again').throw('InvalidStateError');
+
+            // But setting to null is ok.
+            should(function() {
+            }, 'source.buffer = null after setting to null').notThrow();
 
             // Check that mono buffer can be set.
             should(function() {