private ByteBuffer generateContent(List<HttpContent> httpContents) {
    return generateContent(httpContents, false);
  }
Generates random content and fills it up (in parts) in {@code httpContents}.
@param httpContents the {@link List<HttpContent>} that will contain all the content in parts.
@return the whole content as a {@link ByteBuffer} - serves as a source of truth.
ambry-rest/src/test/java/com/github/ambry/rest/NettyRequestTest.java