WebUI: Fix more violations of no-extra-semi lint rule.

chrome/browser/resources/pdf/gesture_detector.js

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 'use strict';
 
 /**
  * A class that listens for touch events and produces events when these
  * touches form gestures (e.g. pinching).
  */
@@ skipping 170 matching lines @@
    * @return {!Object} Midpoint between touch[0] and touch[1].
    */
   static center_(event) {
     let touch1 = event.touches[0];
     let touch2 = event.touches[1];
     return {
       x: (touch1.clientX + touch2.clientX) / 2,
       y: (touch1.clientY + touch2.clientY) / 2
     };
   }
-};
+}