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diff --git a/dom/base/DOMRequestHelper.sys.mjs b/dom/base/DOMRequestHelper.sys.mjs
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+++ b/dom/base/DOMRequestHelper.sys.mjs
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+/* 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/. */
+
+/**
+ * Helper object for APIs that deal with DOMRequests and Promises.
+ * It allows objects inheriting from it to create and keep track of DOMRequests
+ * and Promises objects in the common scenario where requests are created in
+ * the child, handed out to content and delivered to the parent within an async
+ * message (containing the identifiers of these requests). The parent may send
+ * messages back as answers to different requests and the child will use this
+ * helper to get the right request object. This helper also takes care of
+ * releasing the requests objects when the window goes out of scope.
+ *
+ * DOMRequestIPCHelper also deals with message listeners, allowing to add them
+ * to the child side of frame and process message manager and removing them
+ * when needed.
+ */
+export function DOMRequestIpcHelper() {
+  // _listeners keeps a list of messages for which we added a listener and the
+  // kind of listener that we added (strong or weak). It's an object of this
+  // form:
+  //  {
+  //    "message1": true,
+  //    "messagen": false
+  //  }
+  //
+  // where each property is the name of the message and its value is a boolean
+  // that indicates if the listener is weak or not.
+  this._listeners = null;
+  this._requests = null;
+  this._window = null;
+}
+
+DOMRequestIpcHelper.prototype = {
+  /**
+   * An object which "inherits" from DOMRequestIpcHelper and declares its own
+   * queryInterface method MUST implement Ci.nsISupportsWeakReference.
+   */
+  QueryInterface: ChromeUtils.generateQI([
+    "nsISupportsWeakReference",
+    "nsIObserver",
+  ]),
+
+  /**
+   *  'aMessages' is expected to be an array of either:
+   *  - objects of this form:
+   *    {
+   *      name: "messageName",
+   *      weakRef: false
+   *    }
+   *    where 'name' is the message identifier and 'weakRef' a boolean
+   *    indicating if the listener should be a weak referred one or not.
+   *
+   *  - or only strings containing the message name, in which case the listener
+   *    will be added as a strong reference by default.
+   */
+  addMessageListeners(aMessages) {
+    if (!aMessages) {
+      return;
+    }
+
+    if (!this._listeners) {
+      this._listeners = {};
+    }
+
+    if (!Array.isArray(aMessages)) {
+      aMessages = [aMessages];
+    }
+
+    aMessages.forEach(aMsg => {
+      let name = aMsg.name || aMsg;
+      // If the listener is already set and it is of the same type we just
+      // increase the count and bail out. If it is not of the same type,
+      // we throw an exception.
+      if (this._listeners[name] != undefined) {
+        if (!!aMsg.weakRef == this._listeners[name].weakRef) {
+          this._listeners[name].count++;
+          return;
+        }
+        throw Components.Exception("", Cr.NS_ERROR_FAILURE);
+      }
+
+      aMsg.weakRef
+        ? Services.cpmm.addWeakMessageListener(name, this)
+        : Services.cpmm.addMessageListener(name, this);
+      this._listeners[name] = {
+        weakRef: !!aMsg.weakRef,
+        count: 1,
+      };
+    });
+  },
+
+  /**
+   * 'aMessages' is expected to be a string or an array of strings containing
+   * the message names of the listeners to be removed.
+   */
+  removeMessageListeners(aMessages) {
+    if (!this._listeners || !aMessages) {
+      return;
+    }
+
+    if (!Array.isArray(aMessages)) {
+      aMessages = [aMessages];
+    }
+
+    aMessages.forEach(aName => {
+      if (this._listeners[aName] == undefined) {
+        return;
+      }
+
+      // Only remove the listener really when we don't have anybody that could
+      // be waiting on a message.
+      if (!--this._listeners[aName].count) {
+        this._listeners[aName].weakRef
+          ? Services.cpmm.removeWeakMessageListener(aName, this)
+          : Services.cpmm.removeMessageListener(aName, this);
+        delete this._listeners[aName];
+      }
+    });
+  },
+
+  /**
+   * Initialize the helper adding the corresponding listeners to the messages
+   * provided as the second parameter.
+   *
+   * 'aMessages' is expected to be an array of either:
+   *
+   *  - objects of this form:
+   *    {
+   *      name: 'messageName',
+   *      weakRef: false
+   *    }
+   *    where 'name' is the message identifier and 'weakRef' a boolean
+   *    indicating if the listener should be a weak referred one or not.
+   *
+   *  - or only strings containing the message name, in which case the listener
+   *    will be added as a strong referred one by default.
+   */
+  initDOMRequestHelper(aWindow, aMessages) {
+    // Query our required interfaces to force a fast fail if they are not
+    // provided. These calls will throw if the interface is not available.
+    this.QueryInterface(Ci.nsISupportsWeakReference);
+    this.QueryInterface(Ci.nsIObserver);
+
+    if (aMessages) {
+      this.addMessageListeners(aMessages);
+    }
+
+    this._id = this._getRandomId();
+
+    this._window = aWindow;
+    if (this._window) {
+      // We don't use this.innerWindowID, but other classes rely on it.
+      this.innerWindowID = this._window.windowGlobalChild.innerWindowId;
+    }
+
+    this._destroyed = false;
+
+    Services.obs.addObserver(
+      this,
+      "inner-window-destroyed",
+      /* weak-ref */ true
+    );
+  },
+
+  destroyDOMRequestHelper() {
+    if (this._destroyed) {
+      return;
+    }
+
+    this._destroyed = true;
+
+    Services.obs.removeObserver(this, "inner-window-destroyed");
+
+    if (this._listeners) {
+      Object.keys(this._listeners).forEach(aName => {
+        this._listeners[aName].weakRef
+          ? Services.cpmm.removeWeakMessageListener(aName, this)
+          : Services.cpmm.removeMessageListener(aName, this);
+      });
+    }
+
+    this._listeners = null;
+    this._requests = null;
+
+    // Objects inheriting from DOMRequestIPCHelper may have an uninit function.
+    if (this.uninit) {
+      this.uninit();
+    }
+
+    this._window = null;
+  },
+
+  observe(aSubject, aTopic, aData) {
+    if (aTopic !== "inner-window-destroyed") {
+      return;
+    }
+
+    let wId = aSubject.QueryInterface(Ci.nsISupportsPRUint64).data;
+    if (wId != this.innerWindowID) {
+      return;
+    }
+
+    this.destroyDOMRequestHelper();
+  },
+
+  getRequestId(aRequest) {
+    if (!this._requests) {
+      this._requests = {};
+    }
+
+    let id = "id" + this._getRandomId();
+    this._requests[id] = aRequest;
+    return id;
+  },
+
+  getPromiseResolverId(aPromiseResolver) {
+    // Delegates to getRequest() since the lookup table is agnostic about
+    // storage.
+    return this.getRequestId(aPromiseResolver);
+  },
+
+  getRequest(aId) {
+    if (this._requests && this._requests[aId]) {
+      return this._requests[aId];
+    }
+    return undefined;
+  },
+
+  getPromiseResolver(aId) {
+    // Delegates to getRequest() since the lookup table is agnostic about
+    // storage.
+    return this.getRequest(aId);
+  },
+
+  removeRequest(aId) {
+    if (this._requests && this._requests[aId]) {
+      delete this._requests[aId];
+    }
+  },
+
+  removePromiseResolver(aId) {
+    // Delegates to getRequest() since the lookup table is agnostic about
+    // storage.
+    this.removeRequest(aId);
+  },
+
+  takeRequest(aId) {
+    if (!this._requests || !this._requests[aId]) {
+      return null;
+    }
+    let request = this._requests[aId];
+    delete this._requests[aId];
+    return request;
+  },
+
+  takePromiseResolver(aId) {
+    // Delegates to getRequest() since the lookup table is agnostic about
+    // storage.
+    return this.takeRequest(aId);
+  },
+
+  _getRandomId() {
+    return Services.uuid.generateUUID().toString();
+  },
+
+  createRequest() {
+    // If we don't have a valid window object, throw.
+    if (!this._window) {
+      console.error(
+        "DOMRequestHelper trying to create a DOMRequest without a valid window, failing."
+      );
+      throw Components.Exception("", Cr.NS_ERROR_FAILURE);
+    }
+    return Services.DOMRequest.createRequest(this._window);
+  },
+
+  /**
+   * createPromise() creates a new Promise, with `aPromiseInit` as the
+   * PromiseInit callback. The promise constructor is obtained from the
+   * reference to window owned by this DOMRequestIPCHelper.
+   */
+  createPromise(aPromiseInit) {
+    // If we don't have a valid window object, throw.
+    if (!this._window) {
+      console.error(
+        "DOMRequestHelper trying to create a Promise without a valid window, failing."
+      );
+      throw Components.Exception("", Cr.NS_ERROR_FAILURE);
+    }
+    return new this._window.Promise(aPromiseInit);
+  },
+
+  /**
+   * createPromiseWithId() creates a new Promise, accepting a callback
+   * which is immediately called with the generated resolverId.
+   */
+  createPromiseWithId(aCallback) {
+    return this.createPromise((aResolve, aReject) => {
+      let resolverId = this.getPromiseResolverId({
+        resolve: aResolve,
+        reject: aReject,
+      });
+      aCallback(resolverId);
+    });
+  },
+
+  forEachRequest(aCallback) {
+    if (!this._requests) {
+      return;
+    }
+
+    Object.keys(this._requests).forEach(aKey => {
+      if (this._window.DOMRequest.isInstance(this.getRequest(aKey))) {
+        aCallback(aKey);
+      }
+    });
+  },
+
+  forEachPromiseResolver(aCallback) {
+    if (!this._requests) {
+      return;
+    }
+
+    Object.keys(this._requests).forEach(aKey => {
+      if (
+        "resolve" in this.getPromiseResolver(aKey) &&
+        "reject" in this.getPromiseResolver(aKey)
+      ) {
+        aCallback(aKey);
+      }
+    });
+  },
+};