diff --git a/front_end/externs.js b/front_end/externs.js
index 48017b8..eaaf2a7 100644
--- a/front_end/externs.js
+++ b/front_end/externs.js
@@ -1164,3 +1164,315 @@
  * @return {string}
  */
 Lighthouse.ReportGenerator.replaceStrings;
+
+/** @interface */
+class InspectorFrontendHostAPI {
+  /**
+   * @param {string=} type
+   */
+  addFileSystem(type) {
+  }
+
+  loadCompleted() {
+  }
+
+  /**
+   * @param {number} requestId
+   * @param {string} fileSystemPath
+   * @param {string} excludedFolders
+   */
+  indexPath(requestId, fileSystemPath, excludedFolders) {
+  }
+
+  /**
+   * Requests inspected page to be placed atop of the inspector frontend with specified bounds.
+   * @param {{x: number, y: number, width: number, height: number}} bounds
+   */
+  setInspectedPageBounds(bounds) {
+  }
+
+  /**
+   * @param {!Array<string>} certChain
+   */
+  showCertificateViewer(certChain) {
+  }
+
+  /**
+   * @param {string} shortcuts
+   */
+  setWhitelistedShortcuts(shortcuts) {
+  }
+
+  /**
+   * @param {boolean} active
+   */
+  setEyeDropperActive(active) {
+  }
+
+  inspectElementCompleted() {
+  }
+
+  /**
+   * @param {string} url
+   */
+  openInNewTab(url) {
+  }
+
+  /**
+   * @param {string} fileSystemPath
+   */
+  showItemInFolder(fileSystemPath) {
+  }
+
+  /**
+   * @param {string} fileSystemPath
+   */
+  removeFileSystem(fileSystemPath) {
+  }
+
+  requestFileSystems() {
+  }
+
+  /**
+   * @param {string} url
+   * @param {string} content
+   * @param {boolean} forceSaveAs
+   */
+  save(url, content, forceSaveAs) {
+  }
+
+  /**
+   * @param {string} url
+   * @param {string} content
+   */
+  append(url, content) {
+  }
+
+  /**
+   * @param {string} url
+   */
+  close(url) {
+  }
+
+  /**
+   * @param {number} requestId
+   * @param {string} fileSystemPath
+   * @param {string} query
+   */
+  searchInPath(requestId, fileSystemPath, query) {
+  }
+
+  /**
+   * @param {number} requestId
+   */
+  stopIndexing(requestId) {
+  }
+
+  bringToFront() {
+  }
+
+  closeWindow() {
+  }
+
+  copyText(text) {
+  }
+
+  /**
+   * @param {string} url
+   */
+  inspectedURLChanged(url) {
+  }
+
+  /**
+   * @param {string} fileSystemId
+   * @param {string} registeredName
+   * @return {?DOMFileSystem}
+   */
+  isolatedFileSystem(fileSystemId, registeredName) {
+  }
+
+  /**
+   * @param {string} url
+   * @param {string} headers
+   * @param {number} streamId
+   * @param {function(!InspectorFrontendHostAPI.LoadNetworkResourceResult)} callback
+   */
+  loadNetworkResource(url, headers, streamId, callback) {
+  }
+
+  /**
+   * @param {function(!Object<string, string>)} callback
+   */
+  getPreferences(callback) {
+  }
+
+  /**
+   * @param {string} name
+   * @param {string} value
+   */
+  setPreference(name, value) {
+  }
+
+  /**
+   * @param {string} name
+   */
+  removePreference(name) {
+  }
+
+  clearPreferences() {
+  }
+
+  /**
+   * @param {!FileSystem} fileSystem
+   */
+  upgradeDraggedFileSystemPermissions(fileSystem) {
+  }
+
+  /**
+   * @return {string}
+   */
+  platform() {
+  }
+
+  /**
+   * @param {string} actionName
+   * @param {number} actionCode
+   * @param {number} bucketSize
+   */
+  recordEnumeratedHistogram(actionName, actionCode, bucketSize) {
+  }
+
+  /**
+   * @param {string} histogramName
+   * @param {number} duration
+   */
+  recordPerformanceHistogram(histogramName, duration) {
+  }
+
+  /**
+   * @param {string} umaName
+   */
+  recordUserMetricsAction(umaName) {
+  }
+
+  /**
+   * @param {string} message
+   */
+  sendMessageToBackend(message) {
+  }
+
+  /**
+   * @param {!Adb.Config} config
+   */
+  setDevicesDiscoveryConfig(config) {
+  }
+
+  /**
+   * @param {boolean} enabled
+   */
+  setDevicesUpdatesEnabled(enabled) {
+  }
+
+  /**
+   * @param {string} pageId
+   * @param {string} action
+   */
+  performActionOnRemotePage(pageId, action) {
+  }
+
+  /**
+   * @param {string} browserId
+   * @param {string} url
+   */
+  openRemotePage(browserId, url) {
+  }
+
+  openNodeFrontend() {
+  }
+
+  /**
+   * @param {string} origin
+   * @param {string} script
+   */
+  setInjectedScriptForOrigin(origin, script) {
+  }
+
+  /**
+   * @param {boolean} isDocked
+   * @param {function()} callback
+   */
+  setIsDocked(isDocked, callback) {
+  }
+
+  /**
+   * @return {number}
+   */
+  zoomFactor() {
+  }
+
+  zoomIn() {
+  }
+
+  zoomOut() {
+  }
+
+  resetZoom() {
+  }
+
+  /**
+   * @param {number} x
+   * @param {number} y
+   * @param {!Array.<!InspectorFrontendHostAPI.ContextMenuDescriptor>} items
+   * @param {!Document} document
+   */
+  showContextMenuAtPoint(x, y, items, document) {
+  }
+
+  /**
+   * @param {function()} callback
+   */
+  reattach(callback) {
+  }
+
+  readyForTest() {
+  }
+
+  connectionReady() {
+  }
+
+  /**
+   * @param {boolean} value
+   */
+  setOpenNewWindowForPopups(value) {
+  }
+
+  /**
+   * @return {boolean}
+   */
+  isHostedMode() {
+  }
+
+  /**
+   * @param {function(!ExtensionDescriptor)} callback
+   */
+  setAddExtensionCallback(callback) {
+  }
+}
+
+/** @typedef
+{{
+    type: string,
+    id: (number|undefined),
+    label: (string|undefined),
+    enabled: (boolean|undefined),
+    checked: (boolean|undefined),
+    subItems: (!Array.<!InspectorFrontendHostAPI.ContextMenuDescriptor>|undefined)
+}} */
+InspectorFrontendHostAPI.ContextMenuDescriptor;
+
+/** @typedef
+{{
+    statusCode: number,
+    headers: (!Object.<string, string>|undefined)
+}} */
+InspectorFrontendHostAPI.LoadNetworkResourceResult;
\ No newline at end of file