1 files changed, 76 insertions, 0 deletions
diff --git a/devtools/shared/content-observer.js b/devtools/shared/content-observer.js
new file mode 100644
index 0000000000..805037427b
--- /dev/null
+++ b/devtools/shared/content-observer.js
@@ -0,0 +1,76 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+"use strict";
+
+const { Ci } = require("chrome");
+const Services = require("Services");
+
+const EventEmitter = require("devtools/shared/event-emitter");
+
+/**
+ * Handles adding an observer for the creation of content document globals,
+ * event sent immediately after a web content document window has been set up,
+ * but before any script code has been executed.
+ */
+function ContentObserver(targetActor) {
+  this._contentWindow = targetActor.window;
+  this._onContentGlobalCreated = this._onContentGlobalCreated.bind(this);
+  this._onInnerWindowDestroyed = this._onInnerWindowDestroyed.bind(this);
+  this.startListening();
+}
+
+module.exports.ContentObserver = ContentObserver;
+
+ContentObserver.prototype = {
+  /**
+   * Starts listening for the required observer messages.
+   */
+  startListening: function() {
+    Services.obs.addObserver(
+      this._onContentGlobalCreated,
+      "content-document-global-created"
+    );
+    Services.obs.addObserver(
+      this._onInnerWindowDestroyed,
+      "inner-window-destroyed"
+    );
+  },
+
+  /**
+   * Stops listening for the required observer messages.
+   */
+  stopListening: function() {
+    Services.obs.removeObserver(
+      this._onContentGlobalCreated,
+      "content-document-global-created"
+    );
+    Services.obs.removeObserver(
+      this._onInnerWindowDestroyed,
+      "inner-window-destroyed"
+    );
+  },
+
+  /**
+   * Fired immediately after a web content document window has been set up.
+   */
+  _onContentGlobalCreated: function(subject, topic, data) {
+    if (subject == this._contentWindow) {
+      EventEmitter.emit(this, "global-created", subject);
+    }
+  },
+
+  /**
+   * Fired when an inner window is removed from the backward/forward cache.
+   */
+  _onInnerWindowDestroyed: function(subject, topic, data) {
+    const id = subject.QueryInterface(Ci.nsISupportsPRUint64).data;
+    EventEmitter.emit(this, "global-destroyed", id);
+  },
+};
+
+// Utility functions.
+
+ContentObserver.GetInnerWindowID = function(window) {
+  return window.windowGlobalChild.innerWindowId;
+};