Fixes document type detection on iOS 9.

ios/web/web_state/ui/crw_web_controller.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/web/web_state/ui/crw_web_controller.h"
 
 #import <objc/runtime.h>
 #include <cmath>
 
 #include "base/ios/block_types.h"
@@ skipping 3840 matching lines @@
 - (NSString*)externalRequestWindowName {
   if (!_externalRequest || !_externalRequest->window_name)
     return @"";
   return _externalRequest->window_name;
 }
 
 - (void)resetExternalRequest {
   _externalRequest.reset();
 }
 
+- (web::WebViewDocumentType)documentTypeFromMIMEType:(NSString*)MIMEType {
+  if (!MIMEType.length) {
+    return web::WEB_VIEW_DOCUMENT_TYPE_UNKNOWN;
+  }
+
+  if ([MIMEType isEqualToString:@"text/html"] ||
+      [MIMEType isEqualToString:@"application/xhtml+xml"] ||
+      [MIMEType isEqualToString:@"application/xml"]) {
+    return web::WEB_VIEW_DOCUMENT_TYPE_HTML;
+  }
+
+  return web::WEB_VIEW_DOCUMENT_TYPE_GENERIC;
+}
+
 @end