[Workaround] Notify Overscroll Actions that a gesture ended.

ios/chrome/browser/ui/overscroll_actions/overscroll_actions_gesture_recognizer.mm

+// Copyright 2017 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.
+
+#import "ios/chrome/browser/ui/overscroll_actions/overscroll_actions_gesture_recognizer.h"
+
+#import <UIKit/UIGestureRecognizerSubclass.h>
+#include "base/mac/scoped_nsobject.h"

[justincohen, 2017/04/05 14:22:07]

sort?

+
+@interface OverscrollActionsGestureRecognizer () {
+  base::scoped_nsprotocol<id> target_;
+  SEL action_;
+}
+@end
+
+@implementation OverscrollActionsGestureRecognizer
+
+- (instancetype)initWithTarget:(id)target action:(SEL)action {
+  self = [super initWithTarget:target action:action];
+  if (self) {
+    target_.reset([target retain]);
+    action_ = action;
+  }
+  return self;
+}
+
+- (void)reset {
+  [super reset];
+  [target_ performSelector:action_ withObject:self];
+}
+
+- (void)removeTarget:(id)target action:(SEL)action {

[justincohen, 2017/04/05 14:22:07]

This is all voodoo to me.  Why is this necessary? E.g. why is
overscroll_actions_controller::teardown::self.panGestureRecognizer = nil; not
enough?

+  [super removeTarget:target action:action];
+  if (target == target_) {
+    target_.reset();
+  }
+}
+
+@end