Bug 1468754 Part 4: Make ChangesActor fire events. r=pbro

Depends on D9050

Differential Revision: https://phabricator.services.mozilla.com/D9176

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

devtools/server/actors/changes.js

@@ -56,14 +56,18 @@ const ChangesActor = protocol.ActorClassWithSpec(changesSpec, {
 
   pushChange: function(change) {
     this.changes.push(change);
+    this.emit("add-change", change);
   },
 
   popChange: function() {
-    return this.changes.pop();
+    const change = this.changes.pop();
+    this.emit("remove-change", change);
+    return change;
   },
 
   clearChanges: function() {
     this.changes.length = 0;
+    this.emit("clear-changes");
   },
 });
 

devtools/shared/specs/changes.js

@@ -5,6 +5,7 @@
 "use strict";
 
 const {
+  Arg,
   generateActorSpec,
   RetVal,
 } = require("devtools/shared/protocol");
@@ -12,6 +13,20 @@ const {
 const changesSpec = generateActorSpec({
   typeName: "changes",
 
+  events: {
+    "add-change": {
+      type: "addChange",
+      change: Arg(0, "json"),
+    },
+    "remove-change": {
+      type: "removeChange",
+      change: Arg(0, "json"),
+    },
+    "clear-changes": {
+      type: "clearChanges",
+    },
+  },
+
   methods: {
     "allChanges": {
       response: {