Bug 1583749 - Add isDescriptor trait to webextension descriptor actor r=yulia

Depends on D47051.

Without the trait, we keep calling the connect() wrapper on the actor, which is supposed to be deprecated

Differential Revision: https://phabricator.services.mozilla.com/D47053

--HG--
extra : moz-landing-system : lando

devtools/server/actors/descriptors/webextension.js

@@ -83,6 +83,11 @@ const WebExtensionDescriptorActor = protocol.ActorClassWithSpec(
         manifestURL: policy && policy.getURL("manifest.json"),
         name: this.addon.name,
         temporarilyInstalled: this.addon.temporarilyInstalled,
+        traits: {
+          // checked in the front descriptor.
+          // remove when FF70 is on release channel
+          isDescriptor: true,
+        },
         type: this.addon.type,
         url: this.addon.sourceURI ? this.addon.sourceURI.spec : undefined,
         warnings: ExtensionParent.DebugUtils.getExtensionManifestWarnings(
@@ -91,10 +96,6 @@ const WebExtensionDescriptorActor = protocol.ActorClassWithSpec(
       };
     },
 
-    connect() {
-      return this.getTarget();
-    },
-
     getTarget() {
       if (this._childTargetPromise) {
         return this._childTargetPromise;