[WebAudio DevTools] Report graph connection events

This is a follow-up of:
https://chromium-review.googlesource.com/c/chromium/src/+/1724499

This CL introduces new reporting methods to the AudioGraphTracer
class to notify when the graph object connection/disconnection to
the devtool frontend.

The actual reporting code to InspectorWebAudioAgent will be implemented
by the follow-up CLs.

Bug: 970898
Change-Id: Idd00e73f8aec36f2812c4ee60b6bf42d1a2bbd39
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1726957
Commit-Queue: Hongchan Choi <hongchan@chromium.org>
Reviewed-by: Raymond Toy <rtoy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#683210}

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

@@ -49,7 +49,24 @@ class MODULES_EXPORT AudioGraphTracer final
   void DidCreateAudioParam(AudioParam*) {}
   void WillDestroyAudioParam(AudioParam*) {}
 
-  // Notify an associated inspector agent when a BaseAudioContext is changed.
+  // Graph connection events: notifies an associated inspector agent about
+  // when a connection between graph objects happens.
+  void DidConnectNodes(AudioNode* source_node,
+                       AudioNode* destination_node,
+                       unsigned source_output_index = 0,
+                       unsigned destination_input_index = 0) {}
+  void DidDisconnectNodes(AudioNode* source_node,
+                          AudioNode* destination_node = nullptr,
+                          unsigned source_output_index = 0,
+                          unsigned destination_input_index = 0) {}
+  void DidConnectNodeParam(AudioNode* source_node,
+                           AudioParam* destination_param,
+                           unsigned source_output_index = 0) {}
+  void DidDisconnectNodeParam(AudioNode* source_node,
+                              AudioParam* destination_param,
+                              unsigned source_output_index = 0) {}
+
+  // Notifies an associated inspector agent when a BaseAudioContext is changed.
   void DidChangeBaseAudioContext(BaseAudioContext*);
 
   BaseAudioContext* GetContextById(const String contextId);

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

@@ -742,6 +742,8 @@ AudioNode* AudioNode::connect(AudioNode* destination,
 
   Handler().UpdatePullStatusIfNeeded();
 
+  GraphTracer().DidConnectNodes(this, destination, output_index, input_index);
+
   return destination;
 }
 
@@ -784,6 +786,8 @@ void AudioNode::connect(AudioParam* param,
   connected_params_[output_index]->insert(param);
 
   Handler().UpdatePullStatusIfNeeded();
+
+  GraphTracer().DidConnectNodeParam(this, param, output_index);
 }
 
 void AudioNode::DisconnectAllFromOutput(unsigned output_index) {
@@ -825,6 +829,8 @@ void AudioNode::disconnect() {
     DisconnectAllFromOutput(i);
 
   Handler().UpdatePullStatusIfNeeded();
+
+  GraphTracer().DidDisconnectNodes(this);
 }
 
 void AudioNode::disconnect(unsigned output_index,
@@ -846,6 +852,8 @@ void AudioNode::disconnect(unsigned output_index,
   DisconnectAllFromOutput(output_index);
 
   Handler().UpdatePullStatusIfNeeded();
+
+  GraphTracer().DidDisconnectNodes(this, nullptr, output_index);
 }
 
 void AudioNode::disconnect(AudioNode* destination,
@@ -876,6 +884,8 @@ void AudioNode::disconnect(AudioNode* destination,
   }
 
   Handler().UpdatePullStatusIfNeeded();
+
+  GraphTracer().DidDisconnectNodes(this, destination);
 }
 
 void AudioNode::disconnect(AudioNode* destination,
@@ -914,6 +924,8 @@ void AudioNode::disconnect(AudioNode* destination,
   }
 
   Handler().UpdatePullStatusIfNeeded();
+
+  GraphTracer().DidDisconnectNodes(this, destination, output_index);
 }
 
 void AudioNode::disconnect(AudioNode* destination,
@@ -955,6 +967,9 @@ void AudioNode::disconnect(AudioNode* destination,
   }
 
   Handler().UpdatePullStatusIfNeeded();
+
+  GraphTracer().DidDisconnectNodes(
+      this, destination, output_index, input_index);
 }
 
 void AudioNode::disconnect(AudioParam* destination_param,
@@ -981,6 +996,8 @@ void AudioNode::disconnect(AudioParam* destination_param,
   }
 
   Handler().UpdatePullStatusIfNeeded();
+
+  GraphTracer().DidDisconnectNodeParam(this, destination_param);
 }
 
 void AudioNode::disconnect(AudioParam* destination_param,
@@ -1010,6 +1027,8 @@ void AudioNode::disconnect(AudioParam* destination_param,
   }
 
   Handler().UpdatePullStatusIfNeeded();
+
+  GraphTracer().DidDisconnectNodeParam(this, destination_param, output_index);
 }
 
 unsigned AudioNode::numberOfInputs() const {