WriteChannel.capture as implemented by BaseWriteChannel flushes the buffer before capturing. While this seems reasonable to reduce the size of the captured state, it is surprising since the javadoc doesn't mention this at all - intuitively, it does not seem like a method that just captures RestorableState would do blocking I/O, so the javadoc should be extended to clarify this point or the flushing should be removed.

https://github.com/GoogleCloudPlatform/google-cloud-java/blob/master/google-cloud-core/src/main/java/com/google/cloud/WriteChannel.java#L40