Block onScroll if input MotionEvents are null

chrome/android/java/src/org/chromium/chrome/browser/compositor/layouts/eventfilter/GestureEventFilter.java

 // Copyright 2012 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.
 
 package org.chromium.chrome.browser.compositor.layouts.eventfilter;
 
 import android.content.Context;
 import android.os.Handler;
 import android.view.GestureDetector;
 import android.view.MotionEvent;
@@ skipping 80 matching lines @@
         context.getResources();
 
         mDetector = new GestureDetector(context, new GestureDetector.SimpleOnGestureListener() {
 
             private float mOnScrollBeginX;
             private float mOnScrollBeginY;
 
             @Override
             public boolean onScroll(MotionEvent e1, MotionEvent e2,
                     float distanceX, float distanceY) {
+                if (e1 == null || e2 == null) return false;

[Khushal, 2017/04/04 22:10:10]

Could we add a comment here that says this should ideally never happen but is a
workaround, with the bug mentioned?

[mdjones, 2017/04/04 22:16:24]

Done.

+
                 if (!mSeenFirstScrollEvent) {
                     // Remove the touch slop region from the first scroll event to avoid a
                     // jump.
                     mSeenFirstScrollEvent = true;
                     float distance = (float) Math.sqrt(
                             distanceX * distanceX + distanceY * distanceY);
                     if (distance > 0.0f) {
                         float ratio = Math.max(0, distance - mScaledTouchSlop) / distance;
                         mOnScrollBeginX = e1.getX() + distanceX * (1.0f - ratio);
                         mOnScrollBeginY = e1.getY() + distanceY * (1.0f - ratio);
@@ skipping 128 matching lines @@
         }
         mDetector.onTouchEvent(e);
 
         // Propagate the up event after any gesture events.
         if (action == MotionEvent.ACTION_UP || action == MotionEvent.ACTION_CANCEL) {
             mHandler.onUpOrCancel();
         }
         return true;
     }
 }