Use buffer_set flag for AudioBufferSourceNode buffer setter

components/script/dom/audiobuffersourcenode.rs

@@ -29,6 +29,7 @@ use std::f32;
 pub struct AudioBufferSourceNode {
     source_node: AudioScheduledSourceNode,
     buffer: MutNullableDom<AudioBuffer>,
+    buffer_set: Cell<bool>,
     playback_rate: Dom<AudioParam>,
     detune: Dom<AudioParam>,
     loop_enabled: Cell<bool>,
@@ -75,6 +76,7 @@ impl AudioBufferSourceNode {
         let node = AudioBufferSourceNode {
             source_node,
             buffer: Default::default(),
+            buffer_set: Cell::new(false),
             playback_rate: Dom::from_ref(&playback_rate),
             detune: Dom::from_ref(&detune),
             loop_enabled: Cell::new(options.loop_),
@@ -122,12 +124,19 @@ impl AudioBufferSourceNodeMethods for AudioBufferSourceNode {
 
     // https://webaudio.github.io/web-audio-api/#dom-audiobuffersourcenode-buffer
     fn SetBuffer(&self, new_buffer: Option<&AudioBuffer>) -> Fallible<()> {
-        if new_buffer.is_some() && self.buffer.get().is_some() {
-            return Err(Error::InvalidState);
+        if new_buffer.is_some() {
+            if self.buffer_set.get() {
+                // Step 2.
+                return Err(Error::InvalidState);
+            }
+            // Step 3.
+            self.buffer_set.set(true);
         }
 
+        // Step 4.
         self.buffer.set(new_buffer);
 
+        // Step 5.
         if self.source_node.started() {
             if let Some(buffer) = self.buffer.get() {
                 let buffer = buffer.acquire_contents();