From 36d22d82aa202bb199967e9512281e9a53db42c9 Mon Sep 17 00:00:00 2001
From: Daniel Baumann <daniel.baumann@progress-linux.org>
Date: Sun, 7 Apr 2024 21:33:14 +0200
Subject: Adding upstream version 115.7.0esr.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
---
 devtools/server/actors/inspector/walker.js | 2753 ++++++++++++++++++++++++++++
 1 file changed, 2753 insertions(+)
 create mode 100644 devtools/server/actors/inspector/walker.js

(limited to 'devtools/server/actors/inspector/walker.js')

diff --git a/devtools/server/actors/inspector/walker.js b/devtools/server/actors/inspector/walker.js
new file mode 100644
index 0000000000..16250d1e81
--- /dev/null
+++ b/devtools/server/actors/inspector/walker.js
@@ -0,0 +1,2753 @@
+/* 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 { Actor } = require("resource://devtools/shared/protocol.js");
+const { walkerSpec } = require("resource://devtools/shared/specs/walker.js");
+
+const {
+  LongStringActor,
+} = require("resource://devtools/server/actors/string.js");
+const {
+  EXCLUDED_LISTENER,
+} = require("resource://devtools/server/actors/inspector/constants.js");
+
+loader.lazyRequireGetter(
+  this,
+  "nodeFilterConstants",
+  "resource://devtools/shared/dom-node-filter-constants.js"
+);
+
+loader.lazyRequireGetter(
+  this,
+  [
+    "getFrameElement",
+    "isAfterPseudoElement",
+    "isBeforePseudoElement",
+    "isDirectShadowHostChild",
+    "isMarkerPseudoElement",
+    "isFrameBlockedByCSP",
+    "isFrameWithChildTarget",
+    "isShadowHost",
+    "isShadowRoot",
+    "loadSheet",
+  ],
+  "resource://devtools/shared/layout/utils.js",
+  true
+);
+
+loader.lazyRequireGetter(
+  this,
+  "throttle",
+  "resource://devtools/shared/throttle.js",
+  true
+);
+
+loader.lazyRequireGetter(
+  this,
+  [
+    "allAnonymousContentTreeWalkerFilter",
+    "findGridParentContainerForNode",
+    "isNodeDead",
+    "noAnonymousContentTreeWalkerFilter",
+    "nodeDocument",
+    "standardTreeWalkerFilter",
+  ],
+  "resource://devtools/server/actors/inspector/utils.js",
+  true
+);
+
+loader.lazyRequireGetter(
+  this,
+  "CustomElementWatcher",
+  "resource://devtools/server/actors/inspector/custom-element-watcher.js",
+  true
+);
+loader.lazyRequireGetter(
+  this,
+  ["DocumentWalker", "SKIP_TO_SIBLING"],
+  "resource://devtools/server/actors/inspector/document-walker.js",
+  true
+);
+loader.lazyRequireGetter(
+  this,
+  ["NodeActor", "NodeListActor"],
+  "resource://devtools/server/actors/inspector/node.js",
+  true
+);
+loader.lazyRequireGetter(
+  this,
+  "NodePicker",
+  "resource://devtools/server/actors/inspector/node-picker.js",
+  true
+);
+loader.lazyRequireGetter(
+  this,
+  "LayoutActor",
+  "resource://devtools/server/actors/layout.js",
+  true
+);
+loader.lazyRequireGetter(
+  this,
+  ["getLayoutChangesObserver", "releaseLayoutChangesObserver"],
+  "resource://devtools/server/actors/reflow.js",
+  true
+);
+loader.lazyRequireGetter(
+  this,
+  "WalkerSearch",
+  "resource://devtools/server/actors/utils/walker-search.js",
+  true
+);
+
+// ContentDOMReference requires ChromeUtils, which isn't available in worker context.
+const lazy = {};
+if (!isWorker) {
+  loader.lazyGetter(
+    lazy,
+    "ContentDOMReference",
+    () =>
+      ChromeUtils.importESModule(
+        "resource://gre/modules/ContentDOMReference.sys.mjs",
+        {
+          // ContentDOMReference needs to be retrieved from the shared global
+          // since it is a shared singleton.
+          loadInDevToolsLoader: false,
+        }
+      ).ContentDOMReference
+  );
+}
+
+loader.lazyServiceGetter(
+  this,
+  "eventListenerService",
+  "@mozilla.org/eventlistenerservice;1",
+  "nsIEventListenerService"
+);
+
+// Minimum delay between two "new-mutations" events.
+const MUTATIONS_THROTTLING_DELAY = 100;
+// List of mutation types that should -not- be throttled.
+const IMMEDIATE_MUTATIONS = ["pseudoClassLock"];
+
+const HIDDEN_CLASS = "__fx-devtools-hide-shortcut__";
+
+// The possible completions to a ':' with added score to give certain values
+// some preference.
+const PSEUDO_SELECTORS = [
+  [":active", 1],
+  [":hover", 1],
+  [":focus", 1],
+  [":visited", 0],
+  [":link", 0],
+  [":first-letter", 0],
+  [":first-child", 2],
+  [":before", 2],
+  [":after", 2],
+  [":lang(", 0],
+  [":not(", 3],
+  [":first-of-type", 0],
+  [":last-of-type", 0],
+  [":only-of-type", 0],
+  [":only-child", 2],
+  [":nth-child(", 3],
+  [":nth-last-child(", 0],
+  [":nth-of-type(", 0],
+  [":nth-last-of-type(", 0],
+  [":last-child", 2],
+  [":root", 0],
+  [":empty", 0],
+  [":target", 0],
+  [":enabled", 0],
+  [":disabled", 0],
+  [":checked", 1],
+  ["::selection", 0],
+  ["::marker", 0],
+];
+
+const HELPER_SHEET =
+  "data:text/css;charset=utf-8," +
+  encodeURIComponent(`
+  .__fx-devtools-hide-shortcut__ {
+    visibility: hidden !important;
+  }
+`);
+
+/**
+ * We only send nodeValue up to a certain size by default.  This stuff
+ * controls that size.
+ */
+exports.DEFAULT_VALUE_SUMMARY_LENGTH = 50;
+var gValueSummaryLength = exports.DEFAULT_VALUE_SUMMARY_LENGTH;
+
+exports.getValueSummaryLength = function () {
+  return gValueSummaryLength;
+};
+
+exports.setValueSummaryLength = function (val) {
+  gValueSummaryLength = val;
+};
+
+/**
+ * Server side of the DOM walker.
+ */
+class WalkerActor extends Actor {
+  /**
+   * Create the WalkerActor
+   * @param {DevToolsServerConnection} conn
+   *        The server connection.
+   * @param {TargetActor} targetActor
+   *        The top-level Actor for this tab.
+   * @param {Object} options
+   *        - {Boolean} showAllAnonymousContent: Show all native anonymous content
+   */
+  constructor(conn, targetActor, options) {
+    super(conn, walkerSpec);
+    this.targetActor = targetActor;
+    this.rootWin = targetActor.window;
+    this.rootDoc = this.rootWin.document;
+
+    // Map of already created node actors, keyed by their corresponding DOMNode.
+    this._nodeActorsMap = new Map();
+
+    this._pendingMutations = [];
+    this._activePseudoClassLocks = new Set();
+    this._mutationBreakpoints = new WeakMap();
+    this._anonParents = new WeakMap();
+    this.customElementWatcher = new CustomElementWatcher(
+      targetActor.chromeEventHandler
+    );
+
+    // In this map, the key-value pairs are the overflow causing elements and their
+    // respective ancestor scrollable node actor.
+    this.overflowCausingElementsMap = new Map();
+
+    this.showAllAnonymousContent = options.showAllAnonymousContent;
+
+    this.walkerSearch = new WalkerSearch(this);
+
+    // Nodes which have been removed from the client's known
+    // ownership tree are considered "orphaned", and stored in
+    // this set.
+    this._orphaned = new Set();
+
+    // The client can tell the walker that it is interested in a node
+    // even when it is orphaned with the `retainNode` method.  This
+    // list contains orphaned nodes that were so retained.
+    this._retainedOrphans = new Set();
+
+    this.onSubtreeModified = this.onSubtreeModified.bind(this);
+    this.onSubtreeModified[EXCLUDED_LISTENER] = true;
+    this.onNodeRemoved = this.onNodeRemoved.bind(this);
+    this.onNodeRemoved[EXCLUDED_LISTENER] = true;
+    this.onAttributeModified = this.onAttributeModified.bind(this);
+    this.onAttributeModified[EXCLUDED_LISTENER] = true;
+
+    this.onMutations = this.onMutations.bind(this);
+    this.onSlotchange = this.onSlotchange.bind(this);
+    this.onShadowrootattached = this.onShadowrootattached.bind(this);
+    this.onAnonymousrootcreated = this.onAnonymousrootcreated.bind(this);
+    this.onAnonymousrootremoved = this.onAnonymousrootremoved.bind(this);
+    this.onFrameLoad = this.onFrameLoad.bind(this);
+    this.onFrameUnload = this.onFrameUnload.bind(this);
+    this.onCustomElementDefined = this.onCustomElementDefined.bind(this);
+    this._throttledEmitNewMutations = throttle(
+      this._emitNewMutations.bind(this),
+      MUTATIONS_THROTTLING_DELAY
+    );
+
+    targetActor.on("will-navigate", this.onFrameUnload);
+    targetActor.on("window-ready", this.onFrameLoad);
+
+    this.customElementWatcher.on(
+      "element-defined",
+      this.onCustomElementDefined
+    );
+
+    // Keep a reference to the chromeEventHandler for the current targetActor, to make
+    // sure we will be able to remove the listener during the WalkerActor destroy().
+    this.chromeEventHandler = targetActor.chromeEventHandler;
+    // shadowrootattached is a chrome-only event. We enable it below.
+    this.chromeEventHandler.addEventListener(
+      "shadowrootattached",
+      this.onShadowrootattached
+    );
+    // anonymousrootcreated is a chrome-only event. We enable it below.
+    this.chromeEventHandler.addEventListener(
+      "anonymousrootcreated",
+      this.onAnonymousrootcreated
+    );
+    this.chromeEventHandler.addEventListener(
+      "anonymousrootremoved",
+      this.onAnonymousrootremoved
+    );
+    for (const { document } of this.targetActor.windows) {
+      document.devToolsAnonymousAndShadowEventsEnabled = true;
+    }
+
+    // Ensure that the root document node actor is ready and
+    // managed.
+    this.rootNode = this.document();
+
+    this.layoutChangeObserver = getLayoutChangesObserver(this.targetActor);
+    this._onReflows = this._onReflows.bind(this);
+    this.layoutChangeObserver.on("reflows", this._onReflows);
+    this._onResize = this._onResize.bind(this);
+    this.layoutChangeObserver.on("resize", this._onResize);
+
+    this._onEventListenerChange = this._onEventListenerChange.bind(this);
+    eventListenerService.addListenerChangeListener(this._onEventListenerChange);
+  }
+
+  get nodePicker() {
+    if (!this._nodePicker) {
+      this._nodePicker = new NodePicker(this, this.targetActor);
+    }
+
+    return this._nodePicker;
+  }
+
+  watchRootNode() {
+    if (this.rootNode) {
+      this.emit("root-available", this.rootNode);
+    }
+  }
+
+  /**
+   * Callback for eventListenerService.addListenerChangeListener
+   * @param nsISimpleEnumerator changesEnum
+   *    enumerator of nsIEventListenerChange
+   */
+  _onEventListenerChange(changesEnum) {
+    for (const current of changesEnum.enumerate(Ci.nsIEventListenerChange)) {
+      const target = current.target;
+
+      if (this._nodeActorsMap.has(target)) {
+        const actor = this.getNode(target);
+        const mutation = {
+          type: "events",
+          target: actor.actorID,
+          hasEventListeners: actor._hasEventListeners,
+        };
+        this.queueMutation(mutation);
+      }
+    }
+  }
+
+  // Returns the JSON representation of this object over the wire.
+  form() {
+    return {
+      actor: this.actorID,
+      root: this.rootNode.form(),
+      traits: {},
+    };
+  }
+
+  toString() {
+    return "[WalkerActor " + this.actorID + "]";
+  }
+
+  getDocumentWalker(node, skipTo) {
+    // Allow native anon content (like <video> controls) if preffed on
+    const filter = this.showAllAnonymousContent
+      ? allAnonymousContentTreeWalkerFilter
+      : standardTreeWalkerFilter;
+
+    return new DocumentWalker(node, this.rootWin, {
+      filter,
+      skipTo,
+      showAnonymousContent: true,
+    });
+  }
+
+  destroy() {
+    if (this._destroyed) {
+      return;
+    }
+    this._destroyed = true;
+    super.destroy();
+    try {
+      this.clearPseudoClassLocks();
+      this._activePseudoClassLocks = null;
+
+      this.overflowCausingElementsMap.clear();
+      this.overflowCausingElementsMap = null;
+
+      this._hoveredNode = null;
+      this.rootWin = null;
+      this.rootDoc = null;
+      this.rootNode = null;
+      this.layoutHelpers = null;
+      this._orphaned = null;
+      this._retainedOrphans = null;
+      this._nodeActorsMap = null;
+
+      this.targetActor.off("will-navigate", this.onFrameUnload);
+      this.targetActor.off("window-ready", this.onFrameLoad);
+      this.customElementWatcher.off(
+        "element-defined",
+        this.onCustomElementDefined
+      );
+
+      this.chromeEventHandler.removeEventListener(
+        "shadowrootattached",
+        this.onShadowrootattached
+      );
+      this.chromeEventHandler.removeEventListener(
+        "anonymousrootcreated",
+        this.onAnonymousrootcreated
+      );
+      this.chromeEventHandler.removeEventListener(
+        "anonymousrootremoved",
+        this.onAnonymousrootremoved
+      );
+
+      // This attribute is just for devtools, so we can unset once we're done.
+      for (const { document } of this.targetActor.windows) {
+        document.devToolsAnonymousAndShadowEventsEnabled = false;
+      }
+
+      this.onFrameLoad = null;
+      this.onFrameUnload = null;
+
+      this.customElementWatcher.destroy();
+      this.customElementWatcher = null;
+
+      this.walkerSearch.destroy();
+
+      if (this._nodePicker) {
+        this._nodePicker.destroy();
+        this._nodePicker = null;
+      }
+
+      this.layoutChangeObserver.off("reflows", this._onReflows);
+      this.layoutChangeObserver.off("resize", this._onResize);
+      this.layoutChangeObserver = null;
+      releaseLayoutChangesObserver(this.targetActor);
+
+      eventListenerService.removeListenerChangeListener(
+        this._onEventListenerChange
+      );
+
+      this.onMutations = null;
+
+      this.layoutActor = null;
+      this.targetActor = null;
+      this.chromeEventHandler = null;
+
+      this.emit("destroyed");
+    } catch (e) {
+      console.error(e);
+    }
+  }
+
+  release() {}
+
+  unmanage(actor) {
+    if (actor instanceof NodeActor) {
+      if (
+        this._activePseudoClassLocks &&
+        this._activePseudoClassLocks.has(actor)
+      ) {
+        this.clearPseudoClassLocks(actor);
+      }
+
+      this.customElementWatcher.unmanageNode(actor);
+
+      this._nodeActorsMap.delete(actor.rawNode);
+    }
+    super.unmanage(actor);
+  }
+
+  /**
+   * Determine if the walker has come across this DOM node before.
+   * @param {DOMNode} rawNode
+   * @return {Boolean}
+   */
+  hasNode(rawNode) {
+    return this._nodeActorsMap.has(rawNode);
+  }
+
+  /**
+   * If the walker has come across this DOM node before, then get the
+   * corresponding node actor.
+   * @param {DOMNode} rawNode
+   * @return {NodeActor}
+   */
+  getNode(rawNode) {
+    return this._nodeActorsMap.get(rawNode);
+  }
+
+  /**
+   * Internal helper that will either retrieve the existing NodeActor for the
+   * provided node or create the actor on the fly if it doesn't exist.
+   * This method should only be called when we are sure that the node should be
+   * known by the client and that the parent node is already known.
+   *
+   * Otherwise prefer `getNode` to only retrieve known actors or `attachElement`
+   * to create node actors recursively.
+   *
+   * @param  {DOMNode} node
+   *         The node for which we want to create or get an actor
+   * @return {NodeActor} The corresponding NodeActor
+   */
+  _getOrCreateNodeActor(node) {
+    let actor = this.getNode(node);
+    if (actor) {
+      return actor;
+    }
+
+    actor = new NodeActor(this, node);
+
+    // Add the node actor as a child of this walker actor, assigning
+    // it an actorID.
+    this.manage(actor);
+    this._nodeActorsMap.set(node, actor);
+
+    if (node.nodeType === Node.DOCUMENT_NODE) {
+      actor.watchDocument(node, this.onMutations);
+    }
+
+    if (isShadowRoot(actor.rawNode)) {
+      actor.watchDocument(node.ownerDocument, this.onMutations);
+      actor.watchSlotchange(this.onSlotchange);
+    }
+
+    this.customElementWatcher.manageNode(actor);
+
+    return actor;
+  }
+
+  /**
+   * When a custom element is defined, send a customElementDefined mutation for all the
+   * NodeActors using this tag name.
+   */
+  onCustomElementDefined({ name, actors }) {
+    actors.forEach(actor =>
+      this.queueMutation({
+        target: actor.actorID,
+        type: "customElementDefined",
+        customElementLocation: actor.getCustomElementLocation(),
+      })
+    );
+  }
+
+  _onReflows(reflows) {
+    // Going through the nodes the walker knows about, see which ones have had their
+    // display, scrollable or overflow state changed and send events if any.
+    const displayTypeChanges = [];
+    const scrollableStateChanges = [];
+
+    const currentOverflowCausingElementsMap = new Map();
+
+    for (const [node, actor] of this._nodeActorsMap) {
+      if (Cu.isDeadWrapper(node)) {
+        continue;
+      }
+
+      const displayType = actor.displayType;
+      const isDisplayed = actor.isDisplayed;
+
+      if (
+        displayType !== actor.currentDisplayType ||
+        isDisplayed !== actor.wasDisplayed
+      ) {
+        displayTypeChanges.push(actor);
+
+        // Updating the original value
+        actor.currentDisplayType = displayType;
+        actor.wasDisplayed = isDisplayed;
+      }
+
+      const isScrollable = actor.isScrollable;
+      if (isScrollable !== actor.wasScrollable) {
+        scrollableStateChanges.push(actor);
+        actor.wasScrollable = isScrollable;
+      }
+
+      if (isScrollable) {
+        this.updateOverflowCausingElements(
+          actor,
+          currentOverflowCausingElementsMap
+        );
+      }
+    }
+
+    // Get the NodeActor for each node in the symmetric difference of
+    // currentOverflowCausingElementsMap and this.overflowCausingElementsMap
+    const overflowStateChanges = [...currentOverflowCausingElementsMap.keys()]
+      .filter(node => !this.overflowCausingElementsMap.has(node))
+      .concat(
+        [...this.overflowCausingElementsMap.keys()].filter(
+          node => !currentOverflowCausingElementsMap.has(node)
+        )
+      )
+      .filter(node => this.hasNode(node))
+      .map(node => this.getNode(node));
+
+    this.overflowCausingElementsMap = currentOverflowCausingElementsMap;
+
+    if (overflowStateChanges.length) {
+      this.emit("overflow-change", overflowStateChanges);
+    }
+
+    if (displayTypeChanges.length) {
+      this.emit("display-change", displayTypeChanges);
+    }
+
+    if (scrollableStateChanges.length) {
+      this.emit("scrollable-change", scrollableStateChanges);
+    }
+  }
+
+  /**
+   * When the browser window gets resized, relay the event to the front.
+   */
+  _onResize() {
+    this.emit("resize");
+  }
+
+  /**
+   * Ensures that the node is attached and it can be accessed from the root.
+   *
+   * @param {(Node|NodeActor)} nodes The nodes
+   * @return {Object} An object compatible with the disconnectedNode type.
+   */
+  attachElement(node) {
+    const { nodes, newParents } = this.attachElements([node]);
+    return {
+      node: nodes[0],
+      newParents,
+    };
+  }
+
+  /**
+   * Ensures that the nodes are attached and they can be accessed from the root.
+   *
+   * @param {(Node[]|NodeActor[])} nodes The nodes
+   * @return {Object} An object compatible with the disconnectedNodeArray type.
+   */
+  attachElements(nodes) {
+    const nodeActors = [];
+    const newParents = new Set();
+    for (let node of nodes) {
+      if (!(node instanceof NodeActor)) {
+        // If an anonymous node was passed in and we aren't supposed to know
+        // about it, then use the closest ancestor.
+        if (!this.showAllAnonymousContent) {
+          while (
+            node &&
+            standardTreeWalkerFilter(node) != nodeFilterConstants.FILTER_ACCEPT
+          ) {
+            node = this.rawParentNode(node);
+          }
+          if (!node) {
+            continue;
+          }
+        }
+
+        node = this._getOrCreateNodeActor(node);
+      }
+
+      this.ensurePathToRoot(node, newParents);
+      // If nodes may be an array of raw nodes, we're sure to only have
+      // NodeActors with the following array.
+      nodeActors.push(node);
+    }
+
+    return {
+      nodes: nodeActors,
+      newParents: [...newParents],
+    };
+  }
+
+  /**
+   * Return the document node that contains the given node,
+   * or the root node if no node is specified.
+   * @param NodeActor node
+   *        The node whose document is needed, or null to
+   *        return the root.
+   */
+  document(node) {
+    const doc = isNodeDead(node) ? this.rootDoc : nodeDocument(node.rawNode);
+    return this._getOrCreateNodeActor(doc);
+  }
+
+  /**
+   * Return the documentElement for the document containing the
+   * given node.
+   * @param NodeActor node
+   *        The node whose documentElement is requested, or null
+   *        to use the root document.
+   */
+  documentElement(node) {
+    const elt = isNodeDead(node)
+      ? this.rootDoc.documentElement
+      : nodeDocument(node.rawNode).documentElement;
+    return this._getOrCreateNodeActor(elt);
+  }
+
+  parentNode(node) {
+    const parent = this.rawParentNode(node);
+    if (parent) {
+      return this._getOrCreateNodeActor(parent);
+    }
+
+    return null;
+  }
+
+  rawParentNode(node) {
+    const rawNode = node instanceof NodeActor ? node.rawNode : node;
+    if (rawNode == this.rootDoc) {
+      return null;
+    }
+    return InspectorUtils.getParentForNode(rawNode, /* anonymous = */ true);
+  }
+
+  /**
+   * If the given NodeActor only has a single text node as a child with a text
+   * content small enough to be inlined, return that child's NodeActor.
+   *
+   * @param NodeActor node
+   */
+  inlineTextChild({ rawNode }) {
+    // Quick checks to prevent creating a new walker if possible.
+    if (
+      isMarkerPseudoElement(rawNode) ||
+      isBeforePseudoElement(rawNode) ||
+      isAfterPseudoElement(rawNode) ||
+      isShadowHost(rawNode) ||
+      rawNode.nodeType != Node.ELEMENT_NODE ||
+      !!rawNode.children.length ||
+      isFrameWithChildTarget(this.targetActor, rawNode) ||
+      isFrameBlockedByCSP(rawNode)
+    ) {
+      return undefined;
+    }
+
+    const children = this._rawChildren(rawNode, /* includeAssigned = */ true);
+    const firstChild = children[0];
+
+    // Bail out if:
+    // - more than one child
+    // - unique child is not a text node
+    // - unique child is a text node, but is too long to be inlined
+    // - we are a slot -> these are always represented on their own lines with
+    //                    a link to the original node.
+    // - we are a flex item -> these are always shown on their own lines so they can be
+    //                         selected by the flexbox inspector.
+    const isAssignedToSlot =
+      firstChild &&
+      rawNode.nodeName === "SLOT" &&
+      isDirectShadowHostChild(firstChild);
+
+    const isFlexItem = !!firstChild?.parentFlexElement;
+
+    if (
+      !firstChild ||
+      children.length > 1 ||
+      firstChild.nodeType !== Node.TEXT_NODE ||
+      firstChild.nodeValue.length > gValueSummaryLength ||
+      isAssignedToSlot ||
+      isFlexItem
+    ) {
+      return undefined;
+    }
+
+    return this._getOrCreateNodeActor(firstChild);
+  }
+
+  /**
+   * Mark a node as 'retained'.
+   *
+   * A retained node is not released when `releaseNode` is called on its
+   * parent, or when a parent is released with the `cleanup` option to
+   * `getMutations`.
+   *
+   * When a retained node's parent is released, a retained mode is added to
+   * the walker's "retained orphans" list.
+   *
+   * Retained nodes can be deleted by providing the `force` option to
+   * `releaseNode`.  They will also be released when their document
+   * has been destroyed.
+   *
+   * Retaining a node makes no promise about its children;  They can
+   * still be removed by normal means.
+   */
+  retainNode(node) {
+    node.retained = true;
+  }
+
+  /**
+   * Remove the 'retained' mark from a node.  If the node was a
+   * retained orphan, release it.
+   */
+  unretainNode(node) {
+    node.retained = false;
+    if (this._retainedOrphans.has(node)) {
+      this._retainedOrphans.delete(node);
+      this.releaseNode(node);
+    }
+  }
+
+  /**
+   * Release actors for a node and all child nodes.
+   */
+  releaseNode(node, options = {}) {
+    if (isNodeDead(node)) {
+      return;
+    }
+
+    if (node.retained && !options.force) {
+      this._retainedOrphans.add(node);
+      return;
+    }
+
+    if (node.retained) {
+      // Forcing a retained node to go away.
+      this._retainedOrphans.delete(node);
+    }
+
+    for (const child of this._rawChildren(node.rawNode)) {
+      const childActor = this.getNode(child);
+      if (childActor) {
+        this.releaseNode(childActor, options);
+      }
+    }
+
+    node.destroy();
+  }
+
+  /**
+   * Add any nodes between `node` and the walker's root node that have not
+   * yet been seen by the client.
+   */
+  ensurePathToRoot(node, newParents = new Set()) {
+    if (!node) {
+      return newParents;
+    }
+    let parent = this.rawParentNode(node);
+    while (parent) {
+      let parentActor = this.getNode(parent);
+      if (parentActor) {
+        // This parent did exist, so the client knows about it.
+        return newParents;
+      }
+      // This parent didn't exist, so hasn't been seen by the client yet.
+      parentActor = this._getOrCreateNodeActor(parent);
+      newParents.add(parentActor);
+      parent = this.rawParentNode(parentActor);
+    }
+    return newParents;
+  }
+
+  /**
+   * Return the number of children under the provided NodeActor.
+   *
+   * @param NodeActor node
+   *    See JSDoc for children()
+   * @param object options
+   *    See JSDoc for children()
+   * @return Number the number of children
+   */
+  countChildren(node, options = {}) {
+    return this._getChildren(node, options).nodes.length;
+  }
+
+  /**
+   * Return children of the given node.  By default this method will return
+   * all children of the node, but there are options that can restrict this
+   * to a more manageable subset.
+   *
+   * @param NodeActor node
+   *    The node whose children you're curious about.
+   * @param object options
+   *    Named options:
+   *    `maxNodes`: The set of nodes returned by the method will be no longer
+   *       than maxNodes.
+   *    `start`: If a node is specified, the list of nodes will start
+   *       with the given child.  Mutally exclusive with `center`.
+   *    `center`: If a node is specified, the given node will be as centered
+   *       as possible in the list, given how close to the ends of the child
+   *       list it is.  Mutually exclusive with `start`.
+   *
+   * @returns an object with three items:
+   *    hasFirst: true if the first child of the node is included in the list.
+   *    hasLast: true if the last child of the node is included in the list.
+   *    nodes: Array of NodeActor representing the nodes returned by the request.
+   */
+  children(node, options = {}) {
+    const { hasFirst, hasLast, nodes } = this._getChildren(node, options);
+    return {
+      hasFirst,
+      hasLast,
+      nodes: nodes.map(n => this._getOrCreateNodeActor(n)),
+    };
+  }
+
+  /**
+   * Returns the raw children of the DOM node, with anon content filtered as needed
+   * @param Node rawNode.
+   * @param boolean includeAssigned
+   *   Whether <slot> assigned children should be returned. See
+   *   HTMLSlotElement.assignedNodes().
+   * @returns Array<Node> the list of children.
+   */
+  _rawChildren(rawNode, includeAssigned) {
+    const filter = this.showAllAnonymousContent
+      ? allAnonymousContentTreeWalkerFilter
+      : standardTreeWalkerFilter;
+    const ret = [];
+    const children = InspectorUtils.getChildrenForNode(
+      rawNode,
+      /* anonymous = */ true,
+      includeAssigned
+    );
+    for (const child of children) {
+      if (filter(child) == nodeFilterConstants.FILTER_ACCEPT) {
+        ret.push(child);
+      }
+    }
+    return ret;
+  }
+
+  /**
+   * Return chidlren of the given node. Contrary to children children(), this method only
+   * returns DOMNodes. Therefore it will not create NodeActor wrappers and will not
+   * update the nodeActors map for the discovered nodes either. This makes this method
+   * safe to call when you are not sure if the discovered nodes will be communicated to
+   * the client.
+   *
+   * @param NodeActor node
+   *    See JSDoc for children()
+   * @param object options
+   *    See JSDoc for children()
+   * @return  an object with three items:
+   *    hasFirst: true if the first child of the node is included in the list.
+   *    hasLast: true if the last child of the node is included in the list.
+   *    nodes: Array of DOMNodes.
+   */
+  // eslint-disable-next-line complexity
+  _getChildren(node, options = {}) {
+    if (isNodeDead(node) || isFrameBlockedByCSP(node.rawNode)) {
+      return { hasFirst: true, hasLast: true, nodes: [] };
+    }
+
+    if (options.center && options.start) {
+      throw Error("Can't specify both 'center' and 'start' options.");
+    }
+
+    let maxNodes = options.maxNodes || -1;
+    if (maxNodes == -1) {
+      maxNodes = Number.MAX_VALUE;
+    }
+
+    let nodes = this._rawChildren(node.rawNode, /* includeAssigned = */ true);
+    let hasFirst = true;
+    let hasLast = true;
+    if (nodes.length > maxNodes) {
+      let startIndex;
+      if (options.center) {
+        const centerIndex = nodes.indexOf(options.center.rawNode);
+        const backwardCount = Math.floor(maxNodes / 2);
+        // If centering would hit the end, just read the last maxNodes nodes.
+        if (centerIndex - backwardCount + maxNodes >= nodes.length) {
+          startIndex = nodes.length - maxNodes;
+        } else {
+          startIndex = Math.max(0, centerIndex - backwardCount);
+        }
+      } else if (options.start) {
+        startIndex = Math.max(0, nodes.indexOf(options.start.rawNode));
+      } else {
+        startIndex = 0;
+      }
+      const endIndex = Math.min(startIndex + maxNodes, nodes.length);
+      hasFirst = startIndex == 0;
+      hasLast = endIndex >= nodes.length;
+      nodes = nodes.slice(startIndex, endIndex);
+    }
+
+    return { hasFirst, hasLast, nodes };
+  }
+
+  /**
+   * Get the next sibling of a given node.  Getting nodes one at a time
+   * might be inefficient, be careful.
+   */
+  nextSibling(node) {
+    if (isNodeDead(node)) {
+      return null;
+    }
+
+    const walker = this.getDocumentWalker(node.rawNode);
+    const sibling = walker.nextSibling();
+    return sibling ? this._getOrCreateNodeActor(sibling) : null;
+  }
+
+  /**
+   * Get the previous sibling of a given node.  Getting nodes one at a time
+   * might be inefficient, be careful.
+   */
+  previousSibling(node) {
+    if (isNodeDead(node)) {
+      return null;
+    }
+
+    const walker = this.getDocumentWalker(node.rawNode);
+    const sibling = walker.previousSibling();
+    return sibling ? this._getOrCreateNodeActor(sibling) : null;
+  }
+
+  /**
+   * Helper function for the `children` method: Read forward in the sibling
+   * list into an array with `count` items, including the current node.
+   */
+  _readForward(walker, count) {
+    const ret = [];
+
+    let node = walker.currentNode;
+    do {
+      if (!walker.isSkippedNode(node)) {
+        // The walker can be on a node that would be filtered out if it didn't find any
+        // other node to fallback to.
+        ret.push(node);
+      }
+      node = walker.nextSibling();
+    } while (node && --count);
+    return ret;
+  }
+
+  /**
+   * Return the first node in the document that matches the given selector.
+   * See https://developer.mozilla.org/en-US/docs/Web/API/Element.querySelector
+   *
+   * @param NodeActor baseNode
+   * @param string selector
+   */
+  querySelector(baseNode, selector) {
+    if (isNodeDead(baseNode)) {
+      return {};
+    }
+
+    const node = baseNode.rawNode.querySelector(selector);
+    if (!node) {
+      return {};
+    }
+
+    return this.attachElement(node);
+  }
+
+  /**
+   * Return a NodeListActor with all nodes that match the given selector.
+   * See https://developer.mozilla.org/en-US/docs/Web/API/Element.querySelectorAll
+   *
+   * @param NodeActor baseNode
+   * @param string selector
+   */
+  querySelectorAll(baseNode, selector) {
+    let nodeList = null;
+
+    try {
+      nodeList = baseNode.rawNode.querySelectorAll(selector);
+    } catch (e) {
+      // Bad selector. Do nothing as the selector can come from a searchbox.
+    }
+
+    return new NodeListActor(this, nodeList);
+  }
+
+  /**
+   * Get a list of nodes that match the given selector in all known frames of
+   * the current content page.
+   * @param {String} selector.
+   * @return {Array}
+   */
+  _multiFrameQuerySelectorAll(selector) {
+    let nodes = [];
+
+    for (const { document } of this.targetActor.windows) {
+      try {
+        nodes = [...nodes, ...document.querySelectorAll(selector)];
+      } catch (e) {
+        // Bad selector. Do nothing as the selector can come from a searchbox.
+      }
+    }
+
+    return nodes;
+  }
+
+  /**
+   * Get a list of nodes that match the given XPath in all known frames of
+   * the current content page.
+   * @param {String} xPath.
+   * @return {Array}
+   */
+  _multiFrameXPath(xPath) {
+    const nodes = [];
+
+    for (const window of this.targetActor.windows) {
+      const document = window.document;
+      try {
+        const result = document.evaluate(
+          xPath,
+          document.documentElement,
+          null,
+          window.XPathResult.ORDERED_NODE_SNAPSHOT_TYPE,
+          null
+        );
+
+        for (let i = 0; i < result.snapshotLength; i++) {
+          nodes.push(result.snapshotItem(i));
+        }
+      } catch (e) {
+        // Bad XPath. Do nothing as the XPath can come from a searchbox.
+      }
+    }
+
+    return nodes;
+  }
+
+  /**
+   * Return a NodeListActor with all nodes that match the given XPath in all
+   * frames of the current content page.
+   * @param {String} xPath
+   */
+  multiFrameXPath(xPath) {
+    return new NodeListActor(this, this._multiFrameXPath(xPath));
+  }
+
+  /**
+   * Search the document for a given string.
+   * Results will be searched with the walker-search module (searches through
+   * tag names, attribute names and values, and text contents).
+   *
+   * @returns {searchresult}
+   *            - {NodeList} list
+   *            - {Array<Object>} metadata. Extra information with indices that
+   *                              match up with node list.
+   */
+  search(query) {
+    const results = this.walkerSearch.search(query);
+    const nodeList = new NodeListActor(
+      this,
+      results.map(r => r.node)
+    );
+
+    return {
+      list: nodeList,
+      metadata: [],
+    };
+  }
+
+  /**
+   * Returns a list of matching results for CSS selector autocompletion.
+   *
+   * @param string query
+   *        The selector query being completed
+   * @param string completing
+   *        The exact token being completed out of the query
+   * @param string selectorState
+   *        One of "pseudo", "id", "tag", "class", "null"
+   */
+  // eslint-disable-next-line complexity
+  getSuggestionsForQuery(query, completing, selectorState) {
+    const sugs = {
+      classes: new Map(),
+      tags: new Map(),
+      ids: new Map(),
+    };
+    let result = [];
+    let nodes = null;
+    // Filtering and sorting the results so that protocol transfer is miminal.
+    switch (selectorState) {
+      case "pseudo":
+        result = PSEUDO_SELECTORS.filter(item => {
+          return item[0].startsWith(":" + completing);
+        });
+        break;
+
+      case "class":
+        if (!query) {
+          nodes = this._multiFrameQuerySelectorAll("[class]");
+        } else {
+          nodes = this._multiFrameQuerySelectorAll(query);
+        }
+        for (const node of nodes) {
+          for (const className of node.classList) {
+            sugs.classes.set(className, (sugs.classes.get(className) | 0) + 1);
+          }
+        }
+        sugs.classes.delete("");
+        sugs.classes.delete(HIDDEN_CLASS);
+        for (const [className, count] of sugs.classes) {
+          if (className.startsWith(completing)) {
+            result.push(["." + CSS.escape(className), count, selectorState]);
+          }
+        }
+        break;
+
+      case "id":
+        if (!query) {
+          nodes = this._multiFrameQuerySelectorAll("[id]");
+        } else {
+          nodes = this._multiFrameQuerySelectorAll(query);
+        }
+        for (const node of nodes) {
+          sugs.ids.set(node.id, (sugs.ids.get(node.id) | 0) + 1);
+        }
+        for (const [id, count] of sugs.ids) {
+          if (id.startsWith(completing) && id !== "") {
+            result.push(["#" + CSS.escape(id), count, selectorState]);
+          }
+        }
+        break;
+
+      case "tag":
+        if (!query) {
+          nodes = this._multiFrameQuerySelectorAll("*");
+        } else {
+          nodes = this._multiFrameQuerySelectorAll(query);
+        }
+        for (const node of nodes) {
+          const tag = node.localName;
+          sugs.tags.set(tag, (sugs.tags.get(tag) | 0) + 1);
+        }
+        for (const [tag, count] of sugs.tags) {
+          if (new RegExp("^" + completing + ".*", "i").test(tag)) {
+            result.push([tag, count, selectorState]);
+          }
+        }
+
+        // For state 'tag' (no preceding # or .) and when there's no query (i.e.
+        // only one word) then search for the matching classes and ids
+        if (!query) {
+          result = [
+            ...result,
+            ...this.getSuggestionsForQuery(null, completing, "class")
+              .suggestions,
+            ...this.getSuggestionsForQuery(null, completing, "id").suggestions,
+          ];
+        }
+
+        break;
+
+      case "null":
+        nodes = this._multiFrameQuerySelectorAll(query);
+        for (const node of nodes) {
+          sugs.ids.set(node.id, (sugs.ids.get(node.id) | 0) + 1);
+          const tag = node.localName;
+          sugs.tags.set(tag, (sugs.tags.get(tag) | 0) + 1);
+          for (const className of node.classList) {
+            sugs.classes.set(className, (sugs.classes.get(className) | 0) + 1);
+          }
+        }
+        for (const [tag, count] of sugs.tags) {
+          tag && result.push([tag, count]);
+        }
+        for (const [id, count] of sugs.ids) {
+          id && result.push(["#" + id, count]);
+        }
+        sugs.classes.delete("");
+        sugs.classes.delete(HIDDEN_CLASS);
+        for (const [className, count] of sugs.classes) {
+          className && result.push(["." + className, count]);
+        }
+    }
+
+    // Sort by count (desc) and name (asc)
+    result = result.sort((a, b) => {
+      // Computed a sortable string with first the inverted count, then the name
+      let sortA = 10000 - a[1] + a[0];
+      let sortB = 10000 - b[1] + b[0];
+
+      // Prefixing ids, classes and tags, to group results
+      const firstA = a[0].substring(0, 1);
+      const firstB = b[0].substring(0, 1);
+
+      const getSortKeyPrefix = firstLetter => {
+        if (firstLetter === "#") {
+          return "2";
+        }
+        if (firstLetter === ".") {
+          return "1";
+        }
+        return "0";
+      };
+
+      sortA = getSortKeyPrefix(firstA) + sortA;
+      sortB = getSortKeyPrefix(firstB) + sortB;
+
+      // String compare
+      return sortA.localeCompare(sortB);
+    });
+
+    result = result.slice(0, 25);
+
+    return {
+      query,
+      suggestions: result,
+    };
+  }
+
+  /**
+   * Add a pseudo-class lock to a node.
+   *
+   * @param NodeActor node
+   * @param string pseudo
+   *    A pseudoclass: ':hover', ':active', ':focus', ':focus-within'
+   * @param options
+   *    Options object:
+   *    `parents`: True if the pseudo-class should be added
+   *      to parent nodes.
+   *    `enabled`: False if the pseudo-class should be locked
+   *      to 'off'. Defaults to true.
+   *
+   * @returns An empty packet.  A "pseudoClassLock" mutation will
+   *    be queued for any changed nodes.
+   */
+  addPseudoClassLock(node, pseudo, options = {}) {
+    if (isNodeDead(node)) {
+      return;
+    }
+
+    // There can be only one node locked per pseudo, so dismiss all existing
+    // ones
+    for (const locked of this._activePseudoClassLocks) {
+      if (InspectorUtils.hasPseudoClassLock(locked.rawNode, pseudo)) {
+        this._removePseudoClassLock(locked, pseudo);
+      }
+    }
+
+    const enabled = options.enabled === undefined || options.enabled;
+    this._addPseudoClassLock(node, pseudo, enabled);
+
+    if (!options.parents) {
+      return;
+    }
+
+    const walker = this.getDocumentWalker(node.rawNode);
+    let cur;
+    while ((cur = walker.parentNode())) {
+      const curNode = this._getOrCreateNodeActor(cur);
+      this._addPseudoClassLock(curNode, pseudo, enabled);
+    }
+  }
+
+  _queuePseudoClassMutation(node) {
+    this.queueMutation({
+      target: node.actorID,
+      type: "pseudoClassLock",
+      pseudoClassLocks: node.writePseudoClassLocks(),
+    });
+  }
+
+  _addPseudoClassLock(node, pseudo, enabled) {
+    if (node.rawNode.nodeType !== Node.ELEMENT_NODE) {
+      return false;
+    }
+    InspectorUtils.addPseudoClassLock(node.rawNode, pseudo, enabled);
+    this._activePseudoClassLocks.add(node);
+    this._queuePseudoClassMutation(node);
+    return true;
+  }
+
+  hideNode(node) {
+    if (isNodeDead(node)) {
+      return;
+    }
+
+    loadSheet(node.rawNode.ownerGlobal, HELPER_SHEET);
+    node.rawNode.classList.add(HIDDEN_CLASS);
+  }
+
+  unhideNode(node) {
+    if (isNodeDead(node)) {
+      return;
+    }
+
+    node.rawNode.classList.remove(HIDDEN_CLASS);
+  }
+
+  /**
+   * Remove a pseudo-class lock from a node.
+   *
+   * @param NodeActor node
+   * @param string pseudo
+   *    A pseudoclass: ':hover', ':active', ':focus', ':focus-within'
+   * @param options
+   *    Options object:
+   *    `parents`: True if the pseudo-class should be removed
+   *      from parent nodes.
+   *
+   * @returns An empty response.  "pseudoClassLock" mutations
+   *    will be emitted for any changed nodes.
+   */
+  removePseudoClassLock(node, pseudo, options = {}) {
+    if (isNodeDead(node)) {
+      return;
+    }
+
+    this._removePseudoClassLock(node, pseudo);
+
+    // Remove pseudo class for children as we don't want to allow
+    // turning it on for some childs without setting it on some parents
+    for (const locked of this._activePseudoClassLocks) {
+      if (
+        node.rawNode.contains(locked.rawNode) &&
+        InspectorUtils.hasPseudoClassLock(locked.rawNode, pseudo)
+      ) {
+        this._removePseudoClassLock(locked, pseudo);
+      }
+    }
+
+    if (!options.parents) {
+      return;
+    }
+
+    const walker = this.getDocumentWalker(node.rawNode);
+    let cur;
+    while ((cur = walker.parentNode())) {
+      const curNode = this._getOrCreateNodeActor(cur);
+      this._removePseudoClassLock(curNode, pseudo);
+    }
+  }
+
+  _removePseudoClassLock(node, pseudo) {
+    if (node.rawNode.nodeType != Node.ELEMENT_NODE) {
+      return false;
+    }
+    InspectorUtils.removePseudoClassLock(node.rawNode, pseudo);
+    if (!node.writePseudoClassLocks()) {
+      this._activePseudoClassLocks.delete(node);
+    }
+
+    this._queuePseudoClassMutation(node);
+    return true;
+  }
+
+  /**
+   * Clear all the pseudo-classes on a given node or all nodes.
+   * @param {NodeActor} node Optional node to clear pseudo-classes on
+   */
+  clearPseudoClassLocks(node) {
+    if (node && isNodeDead(node)) {
+      return;
+    }
+
+    if (node) {
+      InspectorUtils.clearPseudoClassLocks(node.rawNode);
+      this._activePseudoClassLocks.delete(node);
+      this._queuePseudoClassMutation(node);
+    } else {
+      for (const locked of this._activePseudoClassLocks) {
+        InspectorUtils.clearPseudoClassLocks(locked.rawNode);
+        this._activePseudoClassLocks.delete(locked);
+        this._queuePseudoClassMutation(locked);
+      }
+    }
+  }
+
+  /**
+   * Get a node's innerHTML property.
+   */
+  innerHTML(node) {
+    let html = "";
+    if (!isNodeDead(node)) {
+      html = node.rawNode.innerHTML;
+    }
+    return new LongStringActor(this.conn, html);
+  }
+
+  /**
+   * Set a node's innerHTML property.
+   *
+   * @param {NodeActor} node The node.
+   * @param {string} value The piece of HTML content.
+   */
+  setInnerHTML(node, value) {
+    if (isNodeDead(node)) {
+      return;
+    }
+
+    const rawNode = node.rawNode;
+    if (
+      rawNode.nodeType !== rawNode.ownerDocument.ELEMENT_NODE &&
+      rawNode.nodeType !== rawNode.ownerDocument.DOCUMENT_FRAGMENT_NODE
+    ) {
+      throw new Error("Can only change innerHTML to element or fragment nodes");
+    }
+    // eslint-disable-next-line no-unsanitized/property
+    rawNode.innerHTML = value;
+  }
+
+  /**
+   * Get a node's outerHTML property.
+   *
+   * @param {NodeActor} node The node.
+   */
+  outerHTML(node) {
+    let outerHTML = "";
+    if (!isNodeDead(node)) {
+      outerHTML = node.rawNode.outerHTML;
+    }
+    return new LongStringActor(this.conn, outerHTML);
+  }
+
+  /**
+   * Set a node's outerHTML property.
+   *
+   * @param {NodeActor} node The node.
+   * @param {string} value The piece of HTML content.
+   */
+  setOuterHTML(node, value) {
+    if (isNodeDead(node)) {
+      return;
+    }
+
+    const rawNode = node.rawNode;
+    const doc = nodeDocument(rawNode);
+    const win = doc.defaultView;
+    let parser;
+    if (!win) {
+      throw new Error("The window object shouldn't be null");
+    } else {
+      // We create DOMParser under window object because we want a content
+      // DOMParser, which means all the DOM objects created by this DOMParser
+      // will be in the same DocGroup as rawNode.parentNode. Then the newly
+      // created nodes can be adopted into rawNode.parentNode.
+      parser = new win.DOMParser();
+    }
+
+    const mimeType = rawNode.tagName === "svg" ? "image/svg+xml" : "text/html";
+    const parsedDOM = parser.parseFromString(value, mimeType);
+    const parentNode = rawNode.parentNode;
+
+    // Special case for head and body.  Setting document.body.outerHTML
+    // creates an extra <head> tag, and document.head.outerHTML creates
+    // an extra <body>.  So instead we will call replaceChild with the
+    // parsed DOM, assuming that they aren't trying to set both tags at once.
+    if (rawNode.tagName === "BODY") {
+      if (parsedDOM.head.innerHTML === "") {
+        parentNode.replaceChild(parsedDOM.body, rawNode);
+      } else {
+        // eslint-disable-next-line no-unsanitized/property
+        rawNode.outerHTML = value;
+      }
+    } else if (rawNode.tagName === "HEAD") {
+      if (parsedDOM.body.innerHTML === "") {
+        parentNode.replaceChild(parsedDOM.head, rawNode);
+      } else {
+        // eslint-disable-next-line no-unsanitized/property
+        rawNode.outerHTML = value;
+      }
+    } else if (node.isDocumentElement()) {
+      // Unable to set outerHTML on the document element. Fall back by
+      // setting attributes manually. Then replace all the child nodes.
+      const finalAttributeModifications = [];
+      const attributeModifications = {};
+      for (const attribute of rawNode.attributes) {
+        attributeModifications[attribute.name] = null;
+      }
+      for (const attribute of parsedDOM.documentElement.attributes) {
+        attributeModifications[attribute.name] = attribute.value;
+      }
+      for (const key in attributeModifications) {
+        finalAttributeModifications.push({
+          attributeName: key,
+          newValue: attributeModifications[key],
+        });
+      }
+      node.modifyAttributes(finalAttributeModifications);
+
+      rawNode.replaceChildren(...parsedDOM.firstElementChild.childNodes);
+    } else {
+      // eslint-disable-next-line no-unsanitized/property
+      rawNode.outerHTML = value;
+    }
+  }
+
+  /**
+   * Insert adjacent HTML to a node.
+   *
+   * @param {Node} node
+   * @param {string} position One of "beforeBegin", "afterBegin", "beforeEnd",
+   *                          "afterEnd" (see Element.insertAdjacentHTML).
+   * @param {string} value The HTML content.
+   */
+  insertAdjacentHTML(node, position, value) {
+    if (isNodeDead(node)) {
+      return { node: [], newParents: [] };
+    }
+
+    const rawNode = node.rawNode;
+    const isInsertAsSibling =
+      position === "beforeBegin" || position === "afterEnd";
+
+    // Don't insert anything adjacent to the document element.
+    if (isInsertAsSibling && node.isDocumentElement()) {
+      throw new Error("Can't insert adjacent element to the root.");
+    }
+
+    const rawParentNode = rawNode.parentNode;
+    if (!rawParentNode && isInsertAsSibling) {
+      throw new Error("Can't insert as sibling without parent node.");
+    }
+
+    // We can't use insertAdjacentHTML, because we want to return the nodes
+    // being created (so the front can remove them if the user undoes
+    // the change). So instead, use Range.createContextualFragment().
+    const range = rawNode.ownerDocument.createRange();
+    if (position === "beforeBegin" || position === "afterEnd") {
+      range.selectNode(rawNode);
+    } else {
+      range.selectNodeContents(rawNode);
+    }
+    // eslint-disable-next-line no-unsanitized/method
+    const docFrag = range.createContextualFragment(value);
+    const newRawNodes = Array.from(docFrag.childNodes);
+    switch (position) {
+      case "beforeBegin":
+        rawParentNode.insertBefore(docFrag, rawNode);
+        break;
+      case "afterEnd":
+        // Note: if the second argument is null, rawParentNode.insertBefore
+        // behaves like rawParentNode.appendChild.
+        rawParentNode.insertBefore(docFrag, rawNode.nextSibling);
+        break;
+      case "afterBegin":
+        rawNode.insertBefore(docFrag, rawNode.firstChild);
+        break;
+      case "beforeEnd":
+        rawNode.appendChild(docFrag);
+        break;
+      default:
+        throw new Error(
+          "Invalid position value. Must be either " +
+            "'beforeBegin', 'beforeEnd', 'afterBegin' or 'afterEnd'."
+        );
+    }
+
+    return this.attachElements(newRawNodes);
+  }
+
+  /**
+   * Duplicate a specified node
+   *
+   * @param {NodeActor} node The node to duplicate.
+   */
+  duplicateNode({ rawNode }) {
+    const clonedNode = rawNode.cloneNode(true);
+    rawNode.parentNode.insertBefore(clonedNode, rawNode.nextSibling);
+  }
+
+  /**
+   * Test whether a node is a document or a document element.
+   *
+   * @param {NodeActor} node The node to remove.
+   * @return {boolean} True if the node is a document or a document element.
+   */
+  isDocumentOrDocumentElementNode(node) {
+    return (
+      (node.rawNode.ownerDocument &&
+        node.rawNode.ownerDocument.documentElement === this.rawNode) ||
+      node.rawNode.nodeType === Node.DOCUMENT_NODE
+    );
+  }
+
+  /**
+   * Removes a node from its parent node.
+   *
+   * @param {NodeActor} node The node to remove.
+   * @returns The node's nextSibling before it was removed.
+   */
+  removeNode(node) {
+    if (isNodeDead(node) || this.isDocumentOrDocumentElementNode(node)) {
+      throw Error("Cannot remove document, document elements or dead nodes.");
+    }
+
+    const nextSibling = this.nextSibling(node);
+    node.rawNode.remove();
+    // Mutation events will take care of the rest.
+    return nextSibling;
+  }
+
+  /**
+   * Removes an array of nodes from their parent node.
+   *
+   * @param {NodeActor[]} nodes The nodes to remove.
+   */
+  removeNodes(nodes) {
+    // Check that all nodes are valid before processing the removals.
+    for (const node of nodes) {
+      if (isNodeDead(node) || this.isDocumentOrDocumentElementNode(node)) {
+        throw Error("Cannot remove document, document elements or dead nodes");
+      }
+    }
+
+    for (const node of nodes) {
+      node.rawNode.remove();
+      // Mutation events will take care of the rest.
+    }
+  }
+
+  /**
+   * Insert a node into the DOM.
+   */
+  insertBefore(node, parent, sibling) {
+    if (
+      isNodeDead(node) ||
+      isNodeDead(parent) ||
+      (sibling && isNodeDead(sibling))
+    ) {
+      return;
+    }
+
+    const rawNode = node.rawNode;
+    const rawParent = parent.rawNode;
+    const rawSibling = sibling ? sibling.rawNode : null;
+
+    // Don't bother inserting a node if the document position isn't going
+    // to change. This prevents needless iframes reloading and mutations.
+    if (rawNode.parentNode === rawParent) {
+      let currentNextSibling = this.nextSibling(node);
+      currentNextSibling = currentNextSibling
+        ? currentNextSibling.rawNode
+        : null;
+
+      if (rawNode === rawSibling || currentNextSibling === rawSibling) {
+        return;
+      }
+    }
+
+    rawParent.insertBefore(rawNode, rawSibling);
+  }
+
+  /**
+   * Editing a node's tagname actually means creating a new node with the same
+   * attributes, removing the node and inserting the new one instead.
+   * This method does not return anything as mutation events are taking care of
+   * informing the consumers about changes.
+   */
+  editTagName(node, tagName) {
+    if (isNodeDead(node)) {
+      return null;
+    }
+
+    const oldNode = node.rawNode;
+
+    // Create a new element with the same attributes as the current element and
+    // prepare to replace the current node with it.
+    let newNode;
+    try {
+      newNode = nodeDocument(oldNode).createElement(tagName);
+    } catch (x) {
+      // Failed to create a new element with that tag name, ignore the change,
+      // and signal the error to the front.
+      return Promise.reject(
+        new Error("Could not change node's tagName to " + tagName)
+      );
+    }
+
+    const attrs = oldNode.attributes;
+    for (let i = 0; i < attrs.length; i++) {
+      newNode.setAttribute(attrs[i].name, attrs[i].value);
+    }
+
+    // Insert the new node, and transfer the old node's children.
+    oldNode.parentNode.insertBefore(newNode, oldNode);
+    while (oldNode.firstChild) {
+      newNode.appendChild(oldNode.firstChild);
+    }
+
+    oldNode.remove();
+    return null;
+  }
+
+  /**
+   * Gets the state of the mutation breakpoint types for this actor.
+   *
+   * @param {NodeActor} node The node to get breakpoint info for.
+   */
+  getMutationBreakpoints(node) {
+    let bps;
+    if (!isNodeDead(node)) {
+      bps = this._breakpointInfoForNode(node.rawNode);
+    }
+
+    return (
+      bps || {
+        subtree: false,
+        removal: false,
+        attribute: false,
+      }
+    );
+  }
+
+  /**
+   * Set the state of some subset of mutation breakpoint types for this actor.
+   *
+   * @param {NodeActor} node The node to set breakpoint info for.
+   * @param {Object} bps A subset of the breakpoints for this actor that
+   *                            should be updated to new states.
+   */
+  setMutationBreakpoints(node, bps) {
+    if (isNodeDead(node)) {
+      return;
+    }
+    const rawNode = node.rawNode;
+
+    if (
+      rawNode.ownerDocument &&
+      rawNode.getRootNode({ composed: true }) != rawNode.ownerDocument
+    ) {
+      // We only allow watching for mutations on nodes that are attached to
+      // documents. That allows us to clean up our mutation listeners when all
+      // of the watched nodes have been removed from the document.
+      return;
+    }
+
+    // This argument has nullable fields so we want to only update boolean
+    // field values.
+    const bpsForNode = Object.keys(bps).reduce((obj, bp) => {
+      if (typeof bps[bp] === "boolean") {
+        obj[bp] = bps[bp];
+      }
+      return obj;
+    }, {});
+
+    this._updateMutationBreakpointState("api", rawNode, {
+      ...this.getMutationBreakpoints(node),
+      ...bpsForNode,
+    });
+  }
+
+  /**
+   * Update the mutation breakpoint state for the given DOM node.
+   *
+   * @param {Node} rawNode The DOM node.
+   * @param {Object} bpsForNode The state of each mutation bp type we support.
+   */
+  _updateMutationBreakpointState(mutationReason, rawNode, bpsForNode) {
+    const rawDoc = rawNode.ownerDocument || rawNode;
+
+    const docMutationBreakpoints = this._mutationBreakpointsForDoc(
+      rawDoc,
+      true /* createIfNeeded */
+    );
+    let originalBpsForNode = this._breakpointInfoForNode(rawNode);
+
+    if (!bpsForNode && !originalBpsForNode) {
+      return;
+    }
+
+    bpsForNode = bpsForNode || {};
+    originalBpsForNode = originalBpsForNode || {};
+
+    if (Object.values(bpsForNode).some(Boolean)) {
+      docMutationBreakpoints.nodes.set(rawNode, bpsForNode);
+    } else {
+      docMutationBreakpoints.nodes.delete(rawNode);
+    }
+    if (originalBpsForNode.subtree && !bpsForNode.subtree) {
+      docMutationBreakpoints.counts.subtree -= 1;
+    } else if (!originalBpsForNode.subtree && bpsForNode.subtree) {
+      docMutationBreakpoints.counts.subtree += 1;
+    }
+
+    if (originalBpsForNode.removal && !bpsForNode.removal) {
+      docMutationBreakpoints.counts.removal -= 1;
+    } else if (!originalBpsForNode.removal && bpsForNode.removal) {
+      docMutationBreakpoints.counts.removal += 1;
+    }
+
+    if (originalBpsForNode.attribute && !bpsForNode.attribute) {
+      docMutationBreakpoints.counts.attribute -= 1;
+    } else if (!originalBpsForNode.attribute && bpsForNode.attribute) {
+      docMutationBreakpoints.counts.attribute += 1;
+    }
+
+    this._updateDocumentMutationListeners(rawDoc);
+
+    const actor = this.getNode(rawNode);
+    if (actor) {
+      this.queueMutation({
+        target: actor.actorID,
+        type: "mutationBreakpoint",
+        mutationBreakpoints: this.getMutationBreakpoints(actor),
+        mutationReason,
+      });
+    }
+  }
+
+  /**
+   * Controls whether this DOM document has event listeners attached for
+   * handling of DOM mutation breakpoints.
+   *
+   * @param {Document} rawDoc The DOM document.
+   */
+  _updateDocumentMutationListeners(rawDoc) {
+    const docMutationBreakpoints = this._mutationBreakpointsForDoc(rawDoc);
+    if (!docMutationBreakpoints) {
+      rawDoc.devToolsWatchingDOMMutations = false;
+      return;
+    }
+
+    const anyBreakpoint =
+      docMutationBreakpoints.counts.subtree > 0 ||
+      docMutationBreakpoints.counts.removal > 0 ||
+      docMutationBreakpoints.counts.attribute > 0;
+
+    rawDoc.devToolsWatchingDOMMutations = anyBreakpoint;
+
+    if (docMutationBreakpoints.counts.subtree > 0) {
+      this.chromeEventHandler.addEventListener(
+        "devtoolschildinserted",
+        this.onSubtreeModified,
+        true /* capture */
+      );
+    } else {
+      this.chromeEventHandler.removeEventListener(
+        "devtoolschildinserted",
+        this.onSubtreeModified,
+        true /* capture */
+      );
+    }
+
+    if (anyBreakpoint) {
+      this.chromeEventHandler.addEventListener(
+        "devtoolschildremoved",
+        this.onNodeRemoved,
+        true /* capture */
+      );
+    } else {
+      this.chromeEventHandler.removeEventListener(
+        "devtoolschildremoved",
+        this.onNodeRemoved,
+        true /* capture */
+      );
+    }
+
+    if (docMutationBreakpoints.counts.attribute > 0) {
+      this.chromeEventHandler.addEventListener(
+        "devtoolsattrmodified",
+        this.onAttributeModified,
+        true /* capture */
+      );
+    } else {
+      this.chromeEventHandler.removeEventListener(
+        "devtoolsattrmodified",
+        this.onAttributeModified,
+        true /* capture */
+      );
+    }
+  }
+
+  _breakOnMutation(mutationType, targetNode, ancestorNode, action) {
+    this.targetActor.threadActor.pauseForMutationBreakpoint(
+      mutationType,
+      targetNode,
+      ancestorNode,
+      action
+    );
+  }
+
+  _mutationBreakpointsForDoc(rawDoc, createIfNeeded = false) {
+    let docMutationBreakpoints = this._mutationBreakpoints.get(rawDoc);
+    if (!docMutationBreakpoints && createIfNeeded) {
+      docMutationBreakpoints = {
+        counts: {
+          subtree: 0,
+          removal: 0,
+          attribute: 0,
+        },
+        nodes: new Map(),
+      };
+      this._mutationBreakpoints.set(rawDoc, docMutationBreakpoints);
+    }
+    return docMutationBreakpoints;
+  }
+
+  _breakpointInfoForNode(target) {
+    const docMutationBreakpoints = this._mutationBreakpointsForDoc(
+      target.ownerDocument || target
+    );
+    return (
+      (docMutationBreakpoints && docMutationBreakpoints.nodes.get(target)) ||
+      null
+    );
+  }
+
+  onNodeRemoved(evt) {
+    const mutationBpInfo = this._breakpointInfoForNode(evt.target);
+    const hasNodeRemovalEvent = mutationBpInfo?.removal;
+
+    this._clearMutationBreakpointsFromSubtree(evt.target);
+    if (hasNodeRemovalEvent) {
+      this._breakOnMutation("nodeRemoved", evt.target);
+    } else {
+      this.onSubtreeModified(evt);
+    }
+  }
+
+  onAttributeModified(evt) {
+    const mutationBpInfo = this._breakpointInfoForNode(evt.target);
+    if (mutationBpInfo?.attribute) {
+      this._breakOnMutation("attributeModified", evt.target);
+    }
+  }
+
+  onSubtreeModified(evt) {
+    const action = evt.type === "devtoolschildinserted" ? "add" : "remove";
+    let node = evt.target;
+    if (node.isNativeAnonymous && !this.showAllAnonymousContent) {
+      return;
+    }
+    while ((node = node.parentNode) !== null) {
+      const mutationBpInfo = this._breakpointInfoForNode(node);
+      if (mutationBpInfo?.subtree) {
+        this._breakOnMutation("subtreeModified", evt.target, node, action);
+        break;
+      }
+    }
+  }
+
+  _clearMutationBreakpointsFromSubtree(targetNode) {
+    const targetDoc = targetNode.ownerDocument || targetNode;
+    const docMutationBreakpoints = this._mutationBreakpointsForDoc(targetDoc);
+    if (!docMutationBreakpoints || docMutationBreakpoints.nodes.size === 0) {
+      // Bail early for performance. If the doc has no mutation BPs, there is
+      // no reason to iterate through the children looking for things to detach.
+      return;
+    }
+
+    // The walker is not limited to the subtree of the argument node, so we
+    // need to ensure that we stop walking when we leave the subtree.
+    const nextWalkerSibling = this._getNextTraversalSibling(targetNode);
+
+    const walker = new DocumentWalker(targetNode, this.rootWin, {
+      filter: noAnonymousContentTreeWalkerFilter,
+      skipTo: SKIP_TO_SIBLING,
+    });
+
+    do {
+      this._updateMutationBreakpointState("detach", walker.currentNode, null);
+    } while (walker.nextNode() && walker.currentNode !== nextWalkerSibling);
+  }
+
+  _getNextTraversalSibling(targetNode) {
+    const walker = new DocumentWalker(targetNode, this.rootWin, {
+      filter: noAnonymousContentTreeWalkerFilter,
+      skipTo: SKIP_TO_SIBLING,
+    });
+
+    while (!walker.nextSibling()) {
+      if (!walker.parentNode()) {
+        // If we try to step past the walker root, there is no next sibling.
+        return null;
+      }
+    }
+    return walker.currentNode;
+  }
+
+  /**
+   * Get any pending mutation records.  Must be called by the client after
+   * the `new-mutations` notification is received.  Returns an array of
+   * mutation records.
+   *
+   * Mutation records have a basic structure:
+   *
+   * {
+   *   type: attributes|characterData|childList,
+   *   target: <domnode actor ID>,
+   * }
+   *
+   * And additional attributes based on the mutation type:
+   *
+   * `attributes` type:
+   *   attributeName: <string> - the attribute that changed
+   *   attributeNamespace: <string> - the attribute's namespace URI, if any.
+   *   newValue: <string> - The new value of the attribute, if any.
+   *
+   * `characterData` type:
+   *   newValue: <string> - the new nodeValue for the node
+   *
+   * `childList` type is returned when the set of children for a node
+   * has changed.  Includes extra data, which can be used by the client to
+   * maintain its ownership subtree.
+   *
+   *   added: array of <domnode actor ID> - The list of actors *previously
+   *     seen by the client* that were added to the target node.
+   *   removed: array of <domnode actor ID> The list of actors *previously
+   *     seen by the client* that were removed from the target node.
+   *   inlineTextChild: If the node now has a single text child, it will
+   *     be sent here.
+   *
+   * Actors that are included in a MutationRecord's `removed` but
+   * not in an `added` have been removed from the client's ownership
+   * tree (either by being moved under a node the client has seen yet
+   * or by being removed from the tree entirely), and is considered
+   * 'orphaned'.
+   *
+   * Keep in mind that if a node that the client hasn't seen is moved
+   * into or out of the target node, it will not be included in the
+   * removedNodes and addedNodes list, so if the client is interested
+   * in the new set of children it needs to issue a `children` request.
+   */
+  getMutations(options = {}) {
+    const pending = this._pendingMutations || [];
+    this._pendingMutations = [];
+    this._waitingForGetMutations = false;
+
+    if (options.cleanup) {
+      for (const node of this._orphaned) {
+        // Release the orphaned node.  Nodes or children that have been
+        // retained will be moved to this._retainedOrphans.
+        this.releaseNode(node);
+      }
+      this._orphaned = new Set();
+    }
+
+    return pending;
+  }
+
+  queueMutation(mutation) {
+    if (!this.actorID || this._destroyed) {
+      // We've been destroyed, don't bother queueing this mutation.
+      return;
+    }
+
+    // Add the mutation to the list of mutations to be retrieved next.
+    this._pendingMutations.push(mutation);
+
+    // Bail out if we already emitted a new-mutations event and are waiting for a client
+    // to retrieve them.
+    if (this._waitingForGetMutations) {
+      return;
+    }
+
+    if (IMMEDIATE_MUTATIONS.includes(mutation.type)) {
+      this._emitNewMutations();
+    } else {
+      /**
+       * If many mutations are fired at the same time, clients might sequentially request
+       * children/siblings for updated nodes, which can be costly. By throttling the calls
+       * to getMutations, duplicated mutations will be ignored.
+       */
+      this._throttledEmitNewMutations();
+    }
+  }
+
+  _emitNewMutations() {
+    if (!this.actorID || this._destroyed) {
+      // Bail out if the actor was destroyed after throttling this call.
+      return;
+    }
+
+    if (this._waitingForGetMutations || !this._pendingMutations.length) {
+      // Bail out if we already fired the new-mutation event or if no mutations are
+      // waiting to be retrieved.
+      return;
+    }
+
+    this._waitingForGetMutations = true;
+    this.emit("new-mutations");
+  }
+
+  /**
+   * Handles mutations from the DOM mutation observer API.
+   *
+   * @param array[MutationRecord] mutations
+   *    See https://developer.mozilla.org/en-US/docs/Web/API/MutationObserver#MutationRecord
+   */
+  onMutations(mutations) {
+    // Notify any observers that want *all* mutations (even on nodes that aren't
+    // referenced).  This is not sent over the protocol so can only be used by
+    // scripts running in the server process.
+    this.emit("any-mutation");
+
+    for (const change of mutations) {
+      const targetActor = this.getNode(change.target);
+      if (!targetActor) {
+        continue;
+      }
+      const targetNode = change.target;
+      const type = change.type;
+      const mutation = {
+        type,
+        target: targetActor.actorID,
+      };
+
+      if (type === "attributes") {
+        mutation.attributeName = change.attributeName;
+        mutation.attributeNamespace = change.attributeNamespace || undefined;
+        mutation.newValue = targetNode.hasAttribute(mutation.attributeName)
+          ? targetNode.getAttribute(mutation.attributeName)
+          : null;
+      } else if (type === "characterData") {
+        mutation.newValue = targetNode.nodeValue;
+        this._maybeQueueInlineTextChildMutation(change, targetNode);
+      } else if (type === "childList") {
+        // Get the list of removed and added actors that the client has seen
+        // so that it can keep its ownership tree up to date.
+        const removedActors = [];
+        const addedActors = [];
+        for (const removed of change.removedNodes) {
+          const removedActor = this.getNode(removed);
+          if (!removedActor) {
+            // If the client never encountered this actor we don't need to
+            // mention that it was removed.
+            continue;
+          }
+          // While removed from the tree, nodes are saved as orphaned.
+          this._orphaned.add(removedActor);
+          removedActors.push(removedActor.actorID);
+        }
+        for (const added of change.addedNodes) {
+          const addedActor = this.getNode(added);
+          if (!addedActor) {
+            // If the client never encounted this actor we don't need to tell
+            // it about its addition for ownership tree purposes - if the
+            // client wants to see the new nodes it can ask for children.
+            continue;
+          }
+          // The actor is reconnected to the ownership tree, unorphan
+          // it and let the client know so that its ownership tree is up
+          // to date.
+          this._orphaned.delete(addedActor);
+          addedActors.push(addedActor.actorID);
+        }
+
+        mutation.numChildren = targetActor.numChildren;
+        mutation.removed = removedActors;
+        mutation.added = addedActors;
+
+        const inlineTextChild = this.inlineTextChild(targetActor);
+        if (inlineTextChild) {
+          mutation.inlineTextChild = inlineTextChild.form();
+        }
+      }
+      this.queueMutation(mutation);
+    }
+  }
+
+  /**
+   * Check if the provided mutation could change the way the target element is
+   * inlined with its parent node. If it might, a custom mutation of type
+   * "inlineTextChild" will be queued.
+   *
+   * @param {MutationRecord} mutation
+   *        A characterData type mutation
+   */
+  _maybeQueueInlineTextChildMutation(mutation) {
+    const { oldValue, target } = mutation;
+    const newValue = target.nodeValue;
+    const limit = gValueSummaryLength;
+
+    if (
+      (oldValue.length <= limit && newValue.length <= limit) ||
+      (oldValue.length > limit && newValue.length > limit)
+    ) {
+      // Bail out if the new & old values are both below/above the size limit.
+      return;
+    }
+
+    const parentActor = this.getNode(target.parentNode);
+    if (!parentActor || parentActor.rawNode.children.length) {
+      // If the parent node has other children, a character data mutation will
+      // not change anything regarding inlining text nodes.
+      return;
+    }
+
+    const inlineTextChild = this.inlineTextChild(parentActor);
+    this.queueMutation({
+      type: "inlineTextChild",
+      target: parentActor.actorID,
+      inlineTextChild: inlineTextChild ? inlineTextChild.form() : undefined,
+    });
+  }
+
+  onSlotchange(event) {
+    const target = event.target;
+    const targetActor = this.getNode(target);
+    if (!targetActor) {
+      return;
+    }
+
+    this.queueMutation({
+      type: "slotchange",
+      target: targetActor.actorID,
+    });
+  }
+
+  /**
+   * Fires when an anonymous root is created.
+   * This is needed because regular mutation observers don't fire on some kinds
+   * of NAC creation. We want to treat this like a regular insertion.
+   */
+  onAnonymousrootcreated(event) {
+    const root = event.target;
+    const parent = this.rawParentNode(root);
+    if (!parent) {
+      // These events are async. The node might have been removed already, in
+      // which case there's nothing to do anymore.
+      return;
+    }
+    // By the time onAnonymousrootremoved fires, the node is already detached
+    // from its parent, so we need to remember it by hand.
+    this._anonParents.set(root, parent);
+    this.onMutations([
+      {
+        type: "childList",
+        target: parent,
+        addedNodes: [root],
+        removedNodes: [],
+      },
+    ]);
+  }
+
+  /**
+   * @see onAnonymousrootcreated
+   */
+  onAnonymousrootremoved(event) {
+    const root = event.target;
+    const parent = this._anonParents.get(root);
+    if (!parent) {
+      return;
+    }
+    this._anonParents.delete(root);
+    this.onMutations([
+      {
+        type: "childList",
+        target: parent,
+        addedNodes: [],
+        removedNodes: [root],
+      },
+    ]);
+  }
+
+  onShadowrootattached(event) {
+    const actor = this.getNode(event.target);
+    if (!actor) {
+      return;
+    }
+
+    const mutation = {
+      type: "shadowRootAttached",
+      target: actor.actorID,
+    };
+    this.queueMutation(mutation);
+  }
+
+  onFrameLoad({ window, isTopLevel }) {
+    // By the time we receive the DOMContentLoaded event, we might have been destroyed
+    if (this._destroyed) {
+      return;
+    }
+    const { readyState } = window.document;
+    if (readyState != "interactive" && readyState != "complete") {
+      // The document is not loaded, so we want to register to fire again when the
+      // DOM has been loaded.
+      window.addEventListener(
+        "DOMContentLoaded",
+        this.onFrameLoad.bind(this, { window, isTopLevel }),
+        { once: true }
+      );
+      return;
+    }
+
+    window.document.shadowRootAttachedEventEnabled = true;
+
+    if (isTopLevel) {
+      // If we initialize the inspector while the document is loading,
+      // we may already have a root document set in the constructor.
+      if (
+        this.rootDoc &&
+        this.rootDoc !== window.document &&
+        !Cu.isDeadWrapper(this.rootDoc) &&
+        this.rootDoc.defaultView
+      ) {
+        this.onFrameUnload({ window: this.rootDoc.defaultView });
+      }
+      // Update all DOM objects references to target the new document.
+      this.rootWin = window;
+      this.rootDoc = window.document;
+      this.rootNode = this.document();
+      this.emit("root-available", this.rootNode);
+    } else {
+      const frame = getFrameElement(window);
+      const frameActor = this.getNode(frame);
+      if (frameActor) {
+        // If the parent frame is in the map of known node actors, create the
+        // actor for the new document and emit a root-available event.
+        const documentActor = this._getOrCreateNodeActor(window.document);
+        this.emit("root-available", documentActor);
+      }
+    }
+  }
+
+  // Returns true if domNode is in window or a subframe.
+  _childOfWindow(window, domNode) {
+    while (domNode) {
+      const win = nodeDocument(domNode).defaultView;
+      if (win === window) {
+        return true;
+      }
+      domNode = getFrameElement(win);
+    }
+    return false;
+  }
+
+  onFrameUnload({ window }) {
+    // Any retained orphans that belong to this document
+    // or its children need to be released, and a mutation sent
+    // to notify of that.
+    const releasedOrphans = [];
+
+    for (const retained of this._retainedOrphans) {
+      if (
+        Cu.isDeadWrapper(retained.rawNode) ||
+        this._childOfWindow(window, retained.rawNode)
+      ) {
+        this._retainedOrphans.delete(retained);
+        releasedOrphans.push(retained.actorID);
+        this.releaseNode(retained, { force: true });
+      }
+    }
+
+    if (releasedOrphans.length) {
+      this.queueMutation({
+        target: this.rootNode.actorID,
+        type: "unretained",
+        nodes: releasedOrphans,
+      });
+    }
+
+    const doc = window.document;
+    const documentActor = this.getNode(doc);
+    if (!documentActor) {
+      return;
+    }
+
+    // Removing a frame also removes any mutation breakpoints set on that
+    // document so that clients can clear their set of active breakpoints.
+    const mutationBps = this._mutationBreakpointsForDoc(doc);
+    const nodes = mutationBps ? Array.from(mutationBps.nodes.keys()) : [];
+    for (const node of nodes) {
+      this._updateMutationBreakpointState("unload", node, null);
+    }
+
+    this.emit("root-destroyed", documentActor);
+
+    // Cleanup root doc references if we just unloaded the top level root
+    // document.
+    if (this.rootDoc === doc) {
+      this.rootDoc = null;
+      this.rootNode = null;
+    }
+
+    // Release the actor for the unloaded document.
+    this.releaseNode(documentActor, { force: true });
+  }
+
+  /**
+   * Check if a node is attached to the DOM tree of the current page.
+   * @param {Node} rawNode
+   * @return {Boolean} false if the node is removed from the tree or within a
+   * document fragment
+   */
+  _isInDOMTree(rawNode) {
+    let walker;
+    try {
+      walker = this.getDocumentWalker(rawNode);
+    } catch (e) {
+      // The DocumentWalker may throw NS_ERROR_ILLEGAL_VALUE when the node isn't found as a legit children of its parent
+      // ex: <iframe> manually added as immediate child of another <iframe>
+      if (e.name == "NS_ERROR_ILLEGAL_VALUE") {
+        return false;
+      }
+      throw e;
+    }
+    let current = walker.currentNode;
+
+    // Reaching the top of tree
+    while (walker.parentNode()) {
+      current = walker.currentNode;
+    }
+
+    // The top of the tree is a fragment or is not rootDoc, hence rawNode isn't
+    // attached
+    if (
+      current.nodeType === Node.DOCUMENT_FRAGMENT_NODE ||
+      current !== this.rootDoc
+    ) {
+      return false;
+    }
+
+    // Otherwise the top of the tree is rootDoc, hence rawNode is in rootDoc
+    return true;
+  }
+
+  /**
+   * @see _isInDomTree
+   */
+  isInDOMTree(node) {
+    if (isNodeDead(node)) {
+      return false;
+    }
+    return this._isInDOMTree(node.rawNode);
+  }
+
+  /**
+   * Given a windowID return the NodeActor for the corresponding frameElement,
+   * unless it's the root window
+   */
+  getNodeActorFromWindowID(windowID) {
+    let win;
+
+    try {
+      win = Services.wm.getOuterWindowWithId(windowID);
+    } catch (e) {
+      // ignore
+    }
+
+    if (!win) {
+      return {
+        error: "noWindow",
+        message: "The related docshell is destroyed or not found",
+      };
+    } else if (!win.frameElement) {
+      // the frame element of the root document is privileged & thus
+      // inaccessible, so return the document body/element instead
+      return this.attachElement(
+        win.document.body || win.document.documentElement
+      );
+    }
+
+    return this.attachElement(win.frameElement);
+  }
+
+  /**
+   * Given a contentDomReference return the NodeActor for the corresponding frameElement.
+   */
+  getNodeActorFromContentDomReference(contentDomReference) {
+    let rawNode = lazy.ContentDOMReference.resolve(contentDomReference);
+    if (!rawNode || !this._isInDOMTree(rawNode)) {
+      return null;
+    }
+
+    // This is a special case for the document object whereby it is considered
+    // as document.documentElement (the <html> node)
+    if (rawNode.defaultView && rawNode === rawNode.defaultView.document) {
+      rawNode = rawNode.documentElement;
+    }
+
+    return this.attachElement(rawNode);
+  }
+
+  /**
+   * Given a StyleSheet resource ID, commonly used in the style-editor, get its
+   * ownerNode and return the corresponding walker's NodeActor.
+   * Note that getNodeFromActor was added later and can now be used instead.
+   */
+  getStyleSheetOwnerNode(resourceId) {
+    const manager = this.targetActor.getStyleSheetsManager();
+    const ownerNode = manager.getOwnerNode(resourceId);
+    return this.attachElement(ownerNode);
+  }
+
+  /**
+   * This method can be used to retrieve NodeActor for DOM nodes from other
+   * actors in a way that they can later be highlighted in the page, or
+   * selected in the inspector.
+   * If an actor has a reference to a DOM node, and the UI needs to know about
+   * this DOM node (and possibly select it in the inspector), the UI should
+   * first retrieve a reference to the walkerFront:
+   *
+   * // Make sure the inspector/walker have been initialized first.
+   * const inspectorFront = await toolbox.target.getFront("inspector");
+   * // Retrieve the walker.
+   * const walker = inspectorFront.walker;
+   *
+   * And then call this method:
+   *
+   * // Get the nodeFront from my actor, passing the ID and properties path.
+   * walker.getNodeFromActor(myActorID, ["element"]).then(nodeFront => {
+   *   // Use the nodeFront, e.g. select the node in the inspector.
+   *   toolbox.getPanel("inspector").selection.setNodeFront(nodeFront);
+   * });
+   *
+   * @param {String} actorID The ID for the actor that has a reference to the
+   * DOM node.
+   * @param {Array} path Where, on the actor, is the DOM node stored. If in the
+   * scope of the actor, the node is available as `this.data.node`, then this
+   * should be ["data", "node"].
+   * @return {NodeActor} The attached NodeActor, or null if it couldn't be
+   * found.
+   */
+  getNodeFromActor(actorID, path) {
+    const actor = this.conn.getActor(actorID);
+    if (!actor) {
+      return null;
+    }
+
+    let obj = actor;
+    for (const name of path) {
+      if (!(name in obj)) {
+        return null;
+      }
+      obj = obj[name];
+    }
+
+    return this.attachElement(obj);
+  }
+
+  /**
+   * Returns an instance of the LayoutActor that is used to retrieve CSS layout-related
+   * information.
+   *
+   * @return {LayoutActor}
+   */
+  getLayoutInspector() {
+    if (!this.layoutActor) {
+      this.layoutActor = new LayoutActor(this.conn, this.targetActor, this);
+    }
+
+    return this.layoutActor;
+  }
+
+  /**
+   * Returns the parent grid DOMNode of the given node if it exists, otherwise, it
+   * returns null.
+   */
+  getParentGridNode(node) {
+    if (isNodeDead(node)) {
+      return null;
+    }
+
+    const parentGridNode = findGridParentContainerForNode(node.rawNode);
+    return parentGridNode ? this._getOrCreateNodeActor(parentGridNode) : null;
+  }
+
+  /**
+   * Returns the offset parent DOMNode of the given node if it exists, otherwise, it
+   * returns null.
+   */
+  getOffsetParent(node) {
+    if (isNodeDead(node)) {
+      return null;
+    }
+
+    const offsetParent = node.rawNode.offsetParent;
+
+    if (!offsetParent) {
+      return null;
+    }
+
+    return this._getOrCreateNodeActor(offsetParent);
+  }
+
+  getEmbedderElement(browsingContextID) {
+    const browsingContext = BrowsingContext.get(browsingContextID);
+    let rawNode = browsingContext.embedderElement;
+    if (!this._isInDOMTree(rawNode)) {
+      return null;
+    }
+
+    // This is a special case for the document object whereby it is considered
+    // as document.documentElement (the <html> node)
+    if (rawNode.defaultView && rawNode === rawNode.defaultView.document) {
+      rawNode = rawNode.documentElement;
+    }
+
+    return this.attachElement(rawNode);
+  }
+
+  pick(doFocus, isLocalTab) {
+    this.nodePicker.pick(doFocus, isLocalTab);
+  }
+
+  cancelPick() {
+    this.nodePicker.cancelPick();
+  }
+
+  clearPicker() {
+    this.nodePicker.resetHoveredNodeReference();
+  }
+
+  /**
+   * Given a scrollable node, find its descendants which are causing overflow in it and
+   * add their raw nodes to the map as keys with the scrollable element as the values.
+   *
+   * @param {NodeActor} scrollableNode A scrollable node.
+   * @param {Map} map The map to which the overflow causing elements are added.
+   */
+  updateOverflowCausingElements(scrollableNode, map) {
+    if (
+      isNodeDead(scrollableNode) ||
+      scrollableNode.rawNode.nodeType !== Node.ELEMENT_NODE
+    ) {
+      return;
+    }
+
+    const overflowCausingChildren = [
+      ...InspectorUtils.getOverflowingChildrenOfElement(scrollableNode.rawNode),
+    ];
+
+    for (let overflowCausingChild of overflowCausingChildren) {
+      // overflowCausingChild is a Node, but not necessarily an Element.
+      // So, get the containing Element
+      if (overflowCausingChild.nodeType !== Node.ELEMENT_NODE) {
+        overflowCausingChild = overflowCausingChild.parentElement;
+      }
+      map.set(overflowCausingChild, scrollableNode);
+    }
+  }
+
+  /**
+   * Returns an array of the overflow causing elements' NodeActor for the given node.
+   *
+   * @param {NodeActor} node The scrollable node.
+   * @return {Array<NodeActor>} An array of the overflow causing elements.
+   */
+  getOverflowCausingElements(node) {
+    if (
+      isNodeDead(node) ||
+      node.rawNode.nodeType !== Node.ELEMENT_NODE ||
+      !node.isScrollable
+    ) {
+      return [];
+    }
+
+    const overflowCausingElements = [
+      ...InspectorUtils.getOverflowingChildrenOfElement(node.rawNode),
+    ].map(overflowCausingChild => {
+      if (overflowCausingChild.nodeType !== Node.ELEMENT_NODE) {
+        overflowCausingChild = overflowCausingChild.parentElement;
+      }
+
+      return overflowCausingChild;
+    });
+
+    return this.attachElements(overflowCausingElements);
+  }
+
+  /**
+   * Return the scrollable ancestor node which has overflow because of the given node.
+   *
+   * @param {NodeActor} overflowCausingNode
+   */
+  getScrollableAncestorNode(overflowCausingNode) {
+    if (
+      isNodeDead(overflowCausingNode) ||
+      !this.overflowCausingElementsMap.has(overflowCausingNode.rawNode)
+    ) {
+      return null;
+    }
+
+    return this.overflowCausingElementsMap.get(overflowCausingNode.rawNode);
+  }
+}
+
+exports.WalkerActor = WalkerActor;
-- 
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