Update cronet_client.dart

pkgs/cronet_http/lib/src/cronet_client.dart

@@ -396,6 +396,9 @@ class CronetClient extends BaseClient {
       try {
         data = body.toJByteBuffer();
       } on JniException catch (e) {
+        // There are no unit tests for this code. You can verify this behavior
+        // manually by incrementally increasing the amount of body data in
+        // `CronetClient.post` until you get this exception.
         if (e.message.contains('java.lang.OutOfMemoryError:')) {
           throw ClientException(
               'Not enough memory for request body: ${e.message}', request.url);