Bug 1682780 - [devtools] Remove special hack around ThreadActor.attach from protocol.js internals. r=nchevobbe,jdescottes

This is no longer necessary as attach is no longer entering in a nested event loop.
And so we can have attach to complete and return its value as any other request.

Differential Revision: https://phabricator.services.mozilla.com/D100045

devtools/server/actors/thread.js

@@ -412,11 +412,6 @@ const ThreadActor = ActorClassWithSpec(threadSpec, {
       this.dbg.allowUnobservedAsmJS = !this._options.observeAsmJS;
     }
 
-    // Send the response to the attach request now (rather than
-    // returning it), because protocol.js contains a hack just for this one method.
-    // But this is no longer needed and this can be removed in a dedicated followup.
-    this.conn.send({ from: this.actorID });
-
     // Set everything up so that breakpoint can work
     this._setupForBreaking();
 

devtools/shared/protocol/Actor.js

@@ -176,12 +176,6 @@ var generateRequestHandlers = function(actorSpec, actorProto) {
             // No need to send a response.
             return;
           }
-          // `ThreadActor.attach` manually send the response in middle of its processing
-          // using `DevToolsServerConnection.send` manually. So that it isn't a oneway method,
-          // but we shouldn't try to emit a response here, or it would be duplicated.
-          if (spec.name == "attach" && actorProto.typeName == "thread") {
-            return;
-          }
           if (this.isDestroyed()) {
             console.error(
               `Tried to send a '${spec.name}' method reply on an already destroyed actor` +