[iOS] Upstream changes to swipe recognizer

ios/chrome/browser/ui/side_swipe_gesture_recognizer.h

 // 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.
 
 #ifndef IOS_CHROME_BROWSER_UI_SIDE_SWIPE_GESTURE_RECOGNIZER_H_
 #define IOS_CHROME_BROWSER_UI_SIDE_SWIPE_GESTURE_RECOGNIZER_H_
 
 #import <UIKit/UIGestureRecognizerSubclass.h>
 #import <UIKit/UIKit.h>
 
 // This gesture recognizer is used because the default swipe gesture recognizer
 // is too restrictive.  The default swipe requires a particular velocity and
 // distance that Chrome does not require.
 // Another benefit of using a custom gesture recognizer is it can fail faster,
 // so recognizers that depend on this recognizer can begin faster.
 @interface SideSwipeGestureRecognizer : UIPanGestureRecognizer
 
 // The distance from the edge of the screen in which a side swipe can start.
 @property(nonatomic, assign) CGFloat swipeEdge;
 // The distance from the edge of the screen from which a gesture starts.
 @property(readonly, nonatomic) CGFloat swipeOffset;
+// Starting point of swipe.
+@property(readonly, nonatomic) CGPoint startPoint;
 @property(nonatomic, assign) UISwipeGestureRecognizerDirection direction;
 
 @end
 
 #endif  // IOS_CHROME_BROWSER_UI_SIDE_SWIPE_GESTURE_RECOGNIZER_H_