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 a254291c0b210d52bbffc4e7411cfdcf15a22b97..ea5ca812dc1a2e5095eaabbfb3b6cf985a2de4d0 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
@@ -509,17 +509,8 @@ 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 {