Bug 1687235 - Enable ESLint rule no-setter-return for dom. r=bryce

Differential Revision: https://phabricator.services.mozilla.com/D102155

.eslintrc.js

@@ -662,8 +662,6 @@ module.exports = {
     },
     {
       files: [
-        "dom/base/SlowScriptDebug.jsm",
-        "dom/media/PeerConnection.jsm",
         "mobile/android/chrome/geckoview/SessionStateAggregator.js",
         "mobile/android/modules/geckoview/DelayedInit.jsm",
       ],

dom/base/SlowScriptDebug.jsm

@@ -14,14 +14,14 @@ SlowScriptDebug.prototype = {
     return this._activationHandler;
   },
   set activationHandler(cb) {
-    return (this._activationHandler = cb);
+    this._activationHandler = cb;
   },
 
   get remoteActivationHandler() {
     return this._remoteActivationHandler;
   },
   set remoteActivationHandler(cb) {
-    return (this._remoteActivationHandler = cb);
+    this._remoteActivationHandler = cb;
   },
 };
 

dom/media/PeerConnection.jsm

@@ -856,7 +856,7 @@ class RTCPeerConnection {
         return this.getEH(name);
       },
       set(h) {
-        return this.setEH(name, h);
+        this.setEH(name, h);
       },
     });
   }
@@ -868,7 +868,7 @@ class RTCPeerConnection {
       },
       set(h) {
         this.logWarning(name + " is deprecated! " + msg);
-        return this.setEH(name, h);
+        this.setEH(name, h);
       },
     });
   }