Fix compilation errors.

externs/closure-types.js

@@ -1145,7 +1145,7 @@ Polymer_LegacyElementMixin.prototype.flushDebouncer = function(jobName){};
 */
 Polymer_LegacyElementMixin.prototype.cancelDebouncer = function(jobName){};
 /**
-* @param {Function} callback The callback function to run, bound to `this`.
+* @param {!Function} callback The callback function to run, bound to `this`.
 * @param {number=} waitTime Time to wait before calling the
   `callback`.  If unspecified or 0, the callback will be run at microtask
   timing (before paint).
@@ -1167,18 +1167,18 @@ Polymer_LegacyElementMixin.prototype.cancelAsync = function(handle){};
 Polymer_LegacyElementMixin.prototype.create = function(tag, props){};
 /**
 * @param {string} href URL to document to load.
-* @param {Function} onload Callback to notify when an import successfully
+* @param {!Function=} onload Callback to notify when an import successfully
   loaded.
-* @param {Function} onerror Callback to notify when an import
+* @param {!Function=} onerror Callback to notify when an import
   unsuccessfully loaded.
-* @param {boolean} optAsync True if the import should be loaded `async`.
+* @param {boolean=} optAsync True if the import should be loaded `async`.
   Defaults to `false`.
 * @return {HTMLLinkElement}
 */
 Polymer_LegacyElementMixin.prototype.importHref = function(href, onload, onerror, optAsync){};
 /**
 * @param {string} selector Selector to test.
-* @param {Element=} node Element to test the selector against.
+* @param {!Element=} node Element to test the selector against.
 * @return {boolean}
 */
 Polymer_LegacyElementMixin.prototype.elementMatches = function(selector, node){};
@@ -1320,4 +1320,4 @@ Polymer_ArraySelectorMixin.prototype.select = function(item){};
 * @param {number} idx Index from `items` array to select
 * @return {void}
 */
-Polymer_ArraySelectorMixin.prototype.selectIndex = function(idx){};
+Polymer_ArraySelectorMixin.prototype.selectIndex = function(idx){};

lib/legacy/legacy-element-mixin.html

@@ -517,7 +517,7 @@
        */
       getEffectiveChildren() {
         let list = this.getEffectiveChildNodes();
-        return list.filter(function(/** @type {Node} */ n) {
+        return list.filter(function(/** @type {!Node} */ n) {
           return (n.nodeType === Node.ELEMENT_NODE);
         });
       }

lib/legacy/polymer.dom.html

@@ -17,7 +17,7 @@
 
   const p = Element.prototype;
   /**
-   * @const {function(this:Element, string): boolean}
+   * @const {function(this:Node, string): boolean}
    */
   const normalizedMatchesSelector = p.matches || p.matchesSelector ||
     p.mozMatchesSelector || p.msMatchesSelector ||
@@ -28,7 +28,7 @@
    *
    * @function matchesSelector
    * @memberof Polymer.dom
-   * @param {!Element} node Node to check selector against
+   * @param {!Node} node Node to check selector against
    * @param {string} selector Selector to match
    * @return {boolean} True if node matched selector
    */

lib/utils/gestures.html

@@ -706,7 +706,7 @@
     },
     /**
      * @param {string} type
-     * @param {EventTarget} target
+     * @param {!EventTarget} target
      * @param {Event} event
      * @param {Function} preventer
      * @return {void}
@@ -875,7 +875,7 @@
 
     /**
      * @this {GestureRecognizer}
-     * @param {EventTarget} target
+     * @param {!EventTarget} target
      * @param {Touch} touch
      * @return {void}
      */
@@ -984,6 +984,9 @@
       let dy = Math.abs(e.clientY - this.info.y);
       // find original target from `preventer` for TouchEvents, or `e` for MouseEvents
       let t = Gestures._findOriginalTarget(/** @type {Event} */(preventer || e));
+      if (!t) {
+        return;
+      }
       // dx,dy can be NaN if `click` has been simulated and there was no `down` for `start`
       if (isNaN(dx) || isNaN(dy) || (dx <= TAP_DISTANCE && dy <= TAP_DISTANCE) || isSyntheticClick(e)) {
         // prevent taps from being generated if an event has canceled them

lib/utils/mixin.html

@@ -69,7 +69,7 @@
       return extended;
     }
 
-    return dedupingMixin;
+    return /** @type {T} */ (dedupingMixin);
   };
   /* eslint-enable valid-jsdoc */