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diff --git a/devtools/server/actors/emulation/responsive.js b/devtools/server/actors/emulation/responsive.js
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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/. */
+
+"use strict";
+
+const { Actor } = require("resource://devtools/shared/protocol.js");
+const {
+  responsiveSpec,
+} = require("resource://devtools/shared/specs/responsive.js");
+
+/**
+ * This actor overrides various browser features to simulate different environments to
+ * test how pages perform under various conditions.
+ *
+ * The design below, which saves the previous value of each property before setting, is
+ * needed because it's possible to have multiple copies of this actor for a single page.
+ * When some instance of this actor changes a property, we want it to be able to restore
+ * that property to the way it was found before the change.
+ *
+ * A subtle aspect of the code below is that all get* methods must return non-undefined
+ * values, so that the absence of a previous value can be distinguished from the value for
+ * "no override" for each of the properties.
+ */
+class ResponsiveActor extends Actor {
+  constructor(conn, targetActor) {
+    super(conn, responsiveSpec);
+    this.targetActor = targetActor;
+    this.docShell = targetActor.docShell;
+  }
+
+  destroy() {
+    this.targetActor = null;
+    this.docShell = null;
+
+    super.destroy();
+  }
+
+  get win() {
+    return this.docShell.chromeEventHandler.ownerGlobal;
+  }
+
+  /* Touch events override */
+
+  _previousTouchEventsOverride = undefined;
+
+  /**
+   * Set the current element picker state.
+   *
+   * True means the element picker is currently active and we should not be emulating
+   * touch events.
+   * False means the element picker is not active and it is ok to emulate touch events.
+   *
+   * This actor method is meant to be called by the DevTools front-end. The reason for
+   * this is the following:
+   * RDM is the only current consumer of the touch simulator. RDM instantiates this actor
+   * on its own, whether or not the Toolbox is opened. That means it does so in its own
+   * DevTools Server instance.
+   * When the Toolbox is running, it uses a different DevToolsServer. Therefore, it is not
+   * possible for the touch simulator to know whether the picker is active or not. This
+   * state has to be sent by the client code of the Toolbox to this actor.
+   * If a future use case arises where we want to use the touch simulator from the Toolbox
+   * too, then we could add code in here to detect the picker mode as described in
+   * https://bugzilla.mozilla.org/show_bug.cgi?id=1409085#c3
+
+   * @param {Boolean} state
+   * @param {String} pickerType
+   */
+  setElementPickerState(state, pickerType) {
+    this.targetActor.touchSimulator.setElementPickerState(state, pickerType);
+  }
+
+  /**
+   * Dispatches an "orientationchange" event.
+   */
+  async dispatchOrientationChangeEvent() {
+    const { CustomEvent } = this.win;
+    const orientationChangeEvent = new CustomEvent("orientationchange");
+    this.win.dispatchEvent(orientationChangeEvent);
+  }
+}
+
+exports.ResponsiveActor = ResponsiveActor;