1 files changed, 63 insertions, 0 deletions
diff --git a/devtools/server/actors/resources/reflow.js b/devtools/server/actors/resources/reflow.js
new file mode 100644
index 0000000000..5be9d6e7b2
--- /dev/null
+++ b/devtools/server/actors/resources/reflow.js
@@ -0,0 +1,63 @@
+/* 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 {
+  TYPES: { REFLOW },
+} = require("resource://devtools/server/actors/resources/index.js");
+const Targets = require("resource://devtools/server/actors/targets/index.js");
+
+const {
+  getLayoutChangesObserver,
+  releaseLayoutChangesObserver,
+} = require("resource://devtools/server/actors/reflow.js");
+
+class ReflowWatcher {
+  /**
+   * Start watching for reflows related to a given Target Actor.
+   *
+   * @param TargetActor targetActor
+   *        The target actor from which we should observe reflows
+   * @param Object options
+   *        Dictionary object with following attributes:
+   *        - onAvailable: mandatory function
+   *          This will be called for each resource.
+   */
+  async watch(targetActor, { onAvailable }) {
+    // Only track reflow for non-ParentProcess FRAME targets
+    if (
+      targetActor.targetType !== Targets.TYPES.FRAME ||
+      targetActor.typeName === "parentProcessTarget"
+    ) {
+      return;
+    }
+
+    this._targetActor = targetActor;
+
+    const onReflows = reflows => {
+      onAvailable([
+        {
+          resourceType: REFLOW,
+          reflows,
+        },
+      ]);
+    };
+
+    this._observer = getLayoutChangesObserver(targetActor);
+    this._offReflows = this._observer.on("reflows", onReflows);
+    this._observer.start();
+  }
+
+  destroy() {
+    releaseLayoutChangesObserver(this._targetActor);
+
+    if (this._offReflows) {
+      this._offReflows();
+      this._offReflows = null;
+    }
+  }
+}
+
+module.exports = ReflowWatcher;