Fix a crash bug on deallocation of CWVWebView caused by CWVScrollView.

ios/web_view/shell/shell_view_controller.m

 // Copyright 2014 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/web_view/shell/shell_view_controller.h"
 
 #import <ChromeWebView/ChromeWebView.h>
 #import <MobileCoreServices/MobileCoreServices.h>
 
 #import "ios/web_view/shell/translate_controller.h"
@@ skipping 185 matching lines @@
                        message:@""
                 preferredStyle:UIAlertControllerStyleActionSheet];
 
   [alertController
       addAction:[UIAlertAction actionWithTitle:@"Reload"
                                          style:UIAlertActionStyleDefault
                                        handler:^(UIAlertAction* action) {
                                          [_webView reload];
                                        }]];
 
+  // Removes the web view from the view hierarchy and deallocates it. For
+  // testing deallocation behavior, because there have been multiple crash bugs
+  // on deallocation of CWVWebView.
+  [alertController
+      addAction:[UIAlertAction actionWithTitle:@"Deallocate web view"
+                                         style:UIAlertActionStyleDefault
+                                       handler:^(UIAlertAction* action) {
+                                         [_webView removeFromSuperview];
+                                         _webView = nil;
+                                       }]];
+
   [self presentViewController:alertController animated:YES completion:nil];
 }
 
 - (BOOL)textFieldShouldReturn:(UITextField*)field {
   NSURLRequest* request =
       [NSURLRequest requestWithURL:[NSURL URLWithString:[field text]]];
   [_webView loadRequest:request];
   [field resignFirstResponder];
   [self updateToolbar];
   return YES;
@@ skipping 162 matching lines @@
   // TODO(crbug.com/679895): Add some visual indication that the page load has
   // finished.
   [self updateToolbar];
 }
 
 - (void)webViewWebContentProcessDidTerminate:(CWVWebView*)webView {
   NSLog(@"webViewWebContentProcessDidTerminate");
 }
 
 @end