Fix crash in StaticHTMLNativeContent when deallocating WKWebView on iOS9

ios/chrome/browser/ui/static_content/static_html_native_content.mm

 // 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.
 
 #import "ios/chrome/browser/ui/static_content/static_html_native_content.h"
 
 #include "base/logging.h"
 #import "base/mac/scoped_nsobject.h"
 #import "ios/chrome/browser/ui/overscroll_actions/overscroll_actions_controller.h"
 #include "ios/chrome/browser/ui/static_content/static_html_view_controller.h"
@@ skipping 67 matching lines @@
       rendererInitiated:rendererInitiated];
 }
 
 - (OverscrollActionsController*)overscrollActionsController {
   return _overscrollActionsController.get();
 }
 
 - (void)setOverscrollActionsController:
     (OverscrollActionsController*)controller {
   _overscrollActionsController.reset([controller retain]);
+  [[self scrollView] setDelegate:controller];
 }
 
 #pragma mark -
 #pragma mark CRWNativeContent implementation
 
+- (void)willBeDismissed {
+  [[self scrollView] setDelegate:nil];
+}
+
 - (void)close {
   [_overscrollActionsController invalidate];
 }
 
 - (void)willUpdateSnapshot {
   [_overscrollActionsController clear];
 }
 
 - (const GURL&)url {
   return _URL;
@@ skipping 39 matching lines @@
   if (!_webUsageEnabled) {
     _staticHTMLViewController.reset();
   }
 }
 
 - (UIScrollView*)scrollView {
   return [_staticHTMLViewController scrollView];
 }
 
 @end