Add pending activity to keep Webaudio media nodes alive

MediaStreamSourceNode and related nodes should report they have
activity whenever the context is running, because they actually do.
This prevents the nodes from getting prematurely collected.
Unfortunately, this also means nodes will not be collected until the
context is suspended or stopped.



Bug: 937231
Change-Id: I4cd93fe757d8f34fbbc0c68aeaace4727c77be14
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1496541Reviewed-by: Hongchan Choi <hongchan@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Raymond Toy <rtoy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638306}

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

@@ -193,4 +193,9 @@ void MediaStreamAudioSourceNode::SetFormat(uint32_t number_of_channels,
                                                source_sample_rate);
 }
 
+bool MediaStreamAudioSourceNode::HasPendingActivity() const {
+  // As long as the context is running, this node has activity.
+  return (context()->ContextState() == BaseAudioContext::kRunning);
+}
+
 }  // namespace blink

third_party/blink/renderer/modules/webaudio/media_stream_audio_source_node.h

@@ -77,8 +77,10 @@ class MediaStreamAudioSourceHandler final : public AudioHandler {
   unsigned source_number_of_channels_;
 };
 
-class MediaStreamAudioSourceNode final : public AudioNode,
-                                         public AudioSourceProviderClient {
+class MediaStreamAudioSourceNode final
+    : public AudioNode,
+      public AudioSourceProviderClient,
+      public ActiveScriptWrappable<MediaStreamAudioSourceNode> {
   DEFINE_WRAPPERTYPEINFO();
   USING_GARBAGE_COLLECTED_MIXIN(MediaStreamAudioSourceNode);
 
@@ -101,6 +103,8 @@ class MediaStreamAudioSourceNode final : public AudioNode,
   // AudioSourceProviderClient functions:
   void SetFormat(uint32_t number_of_channels, float sample_rate) override;
 
+  bool HasPendingActivity() const final;
+
  private:
   MediaStreamAudioSourceHandler& GetMediaStreamAudioSourceHandler() const;
 

third_party/blink/renderer/modules/webaudio/media_stream_audio_source_node.idl

@@ -27,7 +27,8 @@
 [
     Constructor(AudioContext context, MediaStreamAudioSourceOptions options),
     RaisesException=Constructor,
-    Measure
+    Measure,
+    ActiveScriptWrappable
 ]
 interface MediaStreamAudioSourceNode : AudioNode {
   [SameObject, ImplementedAs=getMediaStream] readonly attribute MediaStream mediaStream;