Disallow JS execution on WebUI pages.

ios/web/web_state/ui/web_view_js_utils.h

 // 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.
 
 #ifndef IOS_WEB_WEB_STATE_UI_WEB_VIEW_JS_UTILS_H_
 #define IOS_WEB_WEB_STATE_UI_WEB_VIEW_JS_UTILS_H_
 
 #import <Foundation/Foundation.h>
 #include <memory>
 
 #import "ios/web/public/block_types.h"
 
 @class WKWebView;
 
 namespace base {
 class Value;
 }  // namespace base
 
 namespace web {
 
 // The domain for JS evaluation NSErrors in web.
 extern NSString* const kJSEvaluationErrorDomain;
 
 // The maximum recursion depth when parsing JS results.
 extern int const kMaximumParsingRecursionDepth;
 
 // The type of errors that can occur while evaluating JS.
 enum JSEvaluationErrorCode {
   // No web view present to evaluate JS.
-  JS_EVALUATION_ERROR_CODE_NO_WEB_VIEW = 1,
+  JS_EVALUATION_ERROR_CODE_NO_WEB_VIEW = -1000,
+  // JS evaluation is not allowed for security reasons.
+  JS_EVALUATION_ERROR_CODE_REJECTED = -1001,
 };
 
 // Converts result of WKWebView script evaluation to base::Value.
 std::unique_ptr<base::Value> ValueResultFromWKResult(id result);
 
 // Executes JavaScript on WKWebView. If the web view cannot execute JS at the
 // moment, |completion_handler| is called with an NSError.
 void ExecuteJavaScript(WKWebView* web_view,
                        NSString* script,
                        JavaScriptResultBlock completion_handler);
 
 }  // namespace web
 
 #endif  // IOS_WEB_WEB_STATE_UI_WEB_VIEW_JS_UTILS_H_