Handle long press in PDF documents.

chrome/browser/resources/pdf/gesture_detector.js

Index: chrome/browser/resources/pdf/gesture_detector.js
diff --git a/chrome/browser/resources/pdf/gesture_detector.js b/chrome/browser/resources/pdf/gesture_detector.js
index fde4650d92bbbc6db1d8ed7aa7259c90a9e144c3..ba6ce23a26d98b51962ac4530992c2ae61622088 100644
--- a/chrome/browser/resources/pdf/gesture_detector.js
+++ b/chrome/browser/resources/pdf/gesture_detector.js
@@ -19,13 +19,13 @@ class GestureDetector {
     this.element_.addEventListener(
         'touchstart', this.onTouchStart_.bind(this), { passive: false });

[Kevin McNee, 2017/05/02 23:18:18]

Since we're no longer calling preventDefault in this case, this should no longer
be non-passive.
This is updated in my CL, so you can just merge that.

[dsinclair, 2017/05/03 14:18:40]

Yea, I'm going to use your Cl for this bit, I'd done this before I saw your
change.

     this.element_.addEventListener(
-        'touchmove', this.onTouch_.bind(this), { passive: true });
+        '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.touchStartEvent_ = null;
     this.lastEvent_ = null;
 
     this.listeners_ = new Map([
@@ -47,6 +47,14 @@ class GestureDetector {
   }
 
   /**
+   * Returns true if the previous touch start was a two finger touch.
+   * @return {!bool} True if touch start was two finger.

[Kevin McNee, 2017/05/02 23:18:18]

The ! is redundant since booleans are non-nullable. You can just use {boolean}.

[dsinclair, 2017/05/03 14:18:40]

Done.

+   */
+  isTwoFingerTouch() {
+    return this.touchStartEvent_ && this.touchStartEvent_.touches.length == 2;

[Kevin McNee, 2017/05/02 23:18:19]

I notice that |touchStartEvent_| is never cleared even after the gesture ends. I
take it by the time you call this, the current state of the gesture may have
changed.

But then we get that logic at the beginning of onTouch_ which is a bit
unintuitive (there could be a |touchStartEvent_| without a |lastEvent_|).
Perhaps it would be clearer if we just recorded the most recent number of
fingers separately and just stored the events for the gesture detection logic.

[dsinclair, 2017/05/03 14:18:40]

Done.

+  }
+
+  /**
    * Call the relevant listeners with the given |pinchEvent|.
    * @private
    * @param {!Object} pinchEvent The event to notify the listeners of.
@@ -64,11 +72,9 @@ class GestureDetector {
    * @param {!TouchEvent} event Touch event on the element.
    */
   onTouchStart_(event) {
-    // We must preventDefault if there is a two finger touch. By doing so
-    // native pinch-zoom does not interfere with our way of handling the event.
-    if (event.touches.length == 2) {
-      event.preventDefault();
-      this.pinchStartEvent_ = event;
+    this.touchStartEvent_ = event;
+
+    if (this.isTwoFingerTouch()) {
       this.lastEvent_ = event;
       this.notify_({
         type: 'pinchstart',
@@ -83,21 +89,27 @@ class GestureDetector {
    * @param {!TouchEvent} event Touch event on the element.
    */
   onTouch_(event) {
-    if (!this.pinchStartEvent_)
+    // Missing a lastEvent_ means we either haven't got a touchstart or we've
+    // finished handling the pinch already.
+    if (!this.lastEvent_ || !this.isTwoFingerTouch())
       return;
 
+    // Prevent default the touchmove to block the native pinch-zoom.
+    if (event.type == "touchmove")
+      event.preventDefault();

[dsinclair, 2017/05/02 19:44:05]

This is very similar to https://codereview.chromium.org/2847893005/ and will be
updated on top of that CL when it lands.

+
     // Check if the pinch ends with the current event.
     if (event.touches.length < 2 ||
         this.lastEvent_.touches.length !== event.touches.length) {
       let startScaleRatio = GestureDetector.pinchScaleRatio_(
-          this.lastEvent_, this.pinchStartEvent_);
+          this.lastEvent_, this.touchStartEvent_);
       let center = GestureDetector.center_(this.lastEvent_);
       let endEvent = {
         type: 'pinchend',
         startScaleRatio: startScaleRatio,
         center: center
       };
-      this.pinchStartEvent_ = null;
+
       this.lastEvent_ = null;
       this.notify_(endEvent);
       return;
@@ -105,7 +117,7 @@ class GestureDetector {
 
     let scaleRatio = GestureDetector.pinchScaleRatio_(event, this.lastEvent_);
     let startScaleRatio = GestureDetector.pinchScaleRatio_(
-        event, this.pinchStartEvent_);
+        event, this.touchStartEvent_);
     let center = GestureDetector.center_(event);
     this.notify_({
       type: 'pinchupdate',