code: public Blob getResult() {
      while (!isDone()) {
        copyChunk();
      }
      return Blob.fromPb(serviceOptions.getService(), rewriteResponse.result);
    }
docs: Returns the updated information for the written blob. Calling this method when {@code isDone()}
  is {@code false} will block until all pending chunks are copied.
  
  <p>This method has the same effect of doing:
  
  <pre>{@code
  while (!copyWriter.isDone()) {
  copyWriter.copyChunk();
  }
  }</pre>
  
  @throws StorageException upon failure