It seems it should do much more than this in this function, as what Android Webview does.
    @Override
        public InterceptedRequestData shouldInterceptRequest(final String url,
                boolean isMainFrame) {
            InterceptedRequestData interceptedRequestData;
            // Return the response directly if the url is default video poster url.
            interceptedRequestData = mDefaultVideoPosterRequestHandler.shouldInterceptRequest(url);
            if (interceptedRequestData != null) return interceptedRequestData;

            interceptedRequestData = mContentsClient.shouldInterceptRequest(url);

            if (interceptedRequestData == null) {
                mContentsClient.getCallbackHelper().postOnLoadResource(url);
            }

            if (isMainFrame && interceptedRequestData != null &&
                    interceptedRequestData.getData() == null) {
                // In this case the intercepted URLRequest job will simulate an empty response
                // which doesn't trigger the onReceivedError callback. For WebViewClassic
                // compatibility we synthesize that callback. http://crbug.com/180950
                mContentsClient.getCallbackHelper().postOnReceivedError(
                        ErrorCodeConversionHelper.ERROR_UNKNOWN,
                        null /* filled in by the glue layer */, url);
            }
            return interceptedRequestData;
        }'

If they will be added in this patch I think there should be a TODO at least.