Fixes document type detection on iOS 9.

ios/web/web_state/ui/crw_wk_web_view_web_controller.mm

Index: ios/web/web_state/ui/crw_wk_web_view_web_controller.mm
diff --git a/ios/web/web_state/ui/crw_wk_web_view_web_controller.mm b/ios/web/web_state/ui/crw_wk_web_view_web_controller.mm
index 547e9f9fe4fa273f4a5cf9db80465a24388755b6..b7b9ce8c8ed29dae7f2cdefdb0074fbce8073d3a 100644
--- a/ios/web/web_state/ui/crw_wk_web_view_web_controller.mm
+++ b/ios/web/web_state/ui/crw_wk_web_view_web_controller.mm
@@ -536,17 +536,8 @@ WKWebViewErrorSource WKWebViewErrorSourceFromError(NSError* error) {
     return web::WEB_VIEW_DOCUMENT_TYPE_GENERIC;
   }
 
-  std::string mimeType = self.webState->GetContentsMimeType();
-  if (mimeType.empty()) {
-    return web::WEB_VIEW_DOCUMENT_TYPE_UNKNOWN;
-  }
-
-  if (mimeType == "text/html" || mimeType == "application/xhtml+xml" ||
-      mimeType == "application/xml") {
-    return web::WEB_VIEW_DOCUMENT_TYPE_HTML;
-  }
-
-  return web::WEB_VIEW_DOCUMENT_TYPE_GENERIC;
+  std::string MIMEType = self.webState->GetContentsMimeType();
+  return [self documentTypeFromMIMEType:base::SysUTF8ToNSString(MIMEType)];
 }
 
 - (void)loadRequest:(NSMutableURLRequest*)request {