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diff --git a/dom/webidl/HeapSnapshot.webidl b/dom/webidl/HeapSnapshot.webidl
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+/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/.
+ */
+
+/**
+ * A HeapSnapshot represents a snapshot of the heap graph
+ */
+[ChromeOnly, Exposed=(Window,System,Worker)]
+interface HeapSnapshot {
+  /**
+   * A time stamp of when the heap snapshot was taken, if available. Units are
+   * microseconds since midnight (00:00:00) 1 January 1970 UTC.
+   */
+  readonly attribute unsigned long long? creationTime;
+
+  /**
+   * Take a census of the heap snapshot.
+   *
+   * This is the same as |Debugger.Memory.prototype.takeCensus|, but operates on
+   * the offline heap snapshot's serialized heap graph rather than the live heap
+   * graph. The same optional configuration options that can be passed to that
+   * function can be passed here.
+   *
+   * The returned value is determined by the `"breakdown"` option used, and is
+   * usually a `Map`, `Object`, or `Array`. For example, the following breakdown
+   *
+   *     {
+   *       by: "coarseType",
+   *       objects: { by: "objectClass" },
+   *       other:   { by: "internalType" }
+   *     }
+   *
+   * produces a result like this:
+   *
+   *     {
+   *       "objects": {
+   *         "Function":         { "count": 404, "bytes": 37328 },
+   *         "Object":           { "count": 11,  "bytes": 1264 },
+   *         "Debugger":         { "count": 1,   "bytes": 416 },
+   *         "ScriptSource":     { "count": 1,   "bytes": 64 },
+   *         // ... omitted for brevity...
+   *       },
+   *       "scripts":            { "count": 1,   "bytes": 0 },
+   *       "strings":            { "count": 701, "bytes": 49080 },
+   *       "other": {
+   *         "js::Shape":        { "count": 450, "bytes": 0 },
+   *         "js::BaseShape":    { "count": 21,  "bytes": 0 },
+   *         "js::ObjectGroup":  { "count": 17,  "bytes": 0 }
+   *       }
+   *     }
+   *
+   * See the `takeCensus` section of the `js/src/doc/Debugger/Debugger.Memory.md`
+   * file for detailed documentation.
+   */
+  [Throws]
+  any takeCensus(object? options);
+
+  /**
+   * Describe `node` with the specified `breakdown`. See the comment above
+   * `takeCensus` or `js/src/doc/Debugger/Debugger.Memory.md` for detailed
+   * documentation on breakdowns.
+   *
+   * Throws an error when `node` is not the id of a node in the heap snapshot,
+   * or if the breakdown is invalid.
+   */
+  [Throws]
+  any describeNode(object breakdown, NodeId node);
+
+  /**
+   * Compute the dominator tree for this heap snapshot.
+   *
+   * @see DominatorTree.webidl
+   */
+  [Throws]
+  DominatorTree computeDominatorTree();
+
+  /**
+   * Find the shortest retaining paths from the node associated with the ID
+   * `start` to each node associated with the IDs in `targets`. Find at most
+   * `maxNumPaths` retaining paths for each target node.
+   *
+   * The return value is a Map object mapping from each target node ID to an
+   * array of retaining paths. The array may be empty if we did not find any
+   * retaining paths.
+   *
+   * A path is an array of objects of the form:
+   *
+   *     {
+   *         predecessor: <node ID>,
+   *         edge: <string or null>,
+   *     }
+   *
+   * The first `predecessor` will always be `start`. The last edge in the path
+   * leads to the `target` node that is mapped to the path; the `target` does
+   * not appear as a `predecessor` in the path.
+   *
+   * Throws when `start` or any of the elements of `targets` are not an ID of a
+   * node in the snapshot, or if we encounter an out of memory exception.
+   */
+  [Throws]
+  object computeShortestPaths(NodeId start, sequence<NodeId> targets,
+                              unsigned long long maxNumPaths);
+};