Handle long press in PDF documents.

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).
  */
 class GestureDetector {
   /**
    * Constructs a GestureDetector.
    * @param {!Element} element The element to monitor for touch gestures.
    */
   constructor(element) {
     this.element_ = element;
 
     this.element_.addEventListener(
         'touchstart', this.onTouchStart_.bind(this), { passive: true });
     this.element_.addEventListener(
         'touchmove', this.onTouch_.bind(this), { passive: false });
     this.element_.addEventListener(
         'touchend', this.onTouch_.bind(this), { passive: true });
     this.element_.addEventListener(
         'touchcancel', this.onTouch_.bind(this), { passive: true });
 
     this.pinchStartEvent_ = null;
+    this.lastTouchTouchesCount_ = 0;
     this.lastEvent_ = null;
 
     this.listeners_ = new Map([
       ['pinchstart', []],
       ['pinchupdate', []],
       ['pinchend', []]
     ]);
   }
 
   /**
    * Add a |listener| to be notified of |type| events.
    * @param {string} type The event type to be notified for.
    * @param {Function} listener The callback.
    */
   addEventListener(type, listener) {
     if (this.listeners_.has(type)) {
       this.listeners_.get(type).push(listener);
     }
   }
 
   /**
+   * Returns true if the last touch start was a two finger touch.
+   * @return {boolean} True if the last touch start was a two finger touch.
+   */
+  wasTwoFingerTouch() {
+    return this.lastTouchTouchesCount_ == 2;
+  }
+
+  /**
    * Call the relevant listeners with the given |pinchEvent|.
    * @private
    * @param {!Object} pinchEvent The event to notify the listeners of.
    */
   notify_(pinchEvent) {
     let listeners = this.listeners_.get(pinchEvent.type);
 
     for (let l of listeners)
       l(pinchEvent);
   }
 
   /**
    * The callback for touchstart events on the element.
    * @private
    * @param {!TouchEvent} event Touch event on the element.
    */
   onTouchStart_(event) {
-    if (event.touches.length == 2) {
-      this.pinchStartEvent_ = event;
-      this.lastEvent_ = event;
-      this.notify_({
-        type: 'pinchstart',
-        center: GestureDetector.center_(event)
-      });
-    }
+    this.lastTouchTouchesCount_ = event.touches.length;
+    if (!this.wasTwoFingerTouch())
+      return;
+
+    this.pinchStartEvent_ = event;
+    this.lastEvent_ = event;
+    this.notify_({
+      type: 'pinchstart',
+      center: GestureDetector.center_(event)
+    });
   }
 
   /**
    * The callback for touch move, end, and cancel events on the element.
    * @private
    * @param {!TouchEvent} event Touch event on the element.
    */
   onTouch_(event) {
     if (!this.pinchStartEvent_)
       return;
@@ skipping 71 matching lines @@
    */
   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
     };
   }
 };