Splits a Blob into chunks of size BLOB_CHUNK_SIZE.

def _BlobToChunks(blob_id, blob):
  """Splits a Blob into chunks of size BLOB_CHUNK_SIZE."""
  #  In case of empty blob (with empty range), use [0].
  chunk_begins = list(range(0, len(blob), BLOB_CHUNK_SIZE)) or [0]
  chunks = []
  for i, chunk_begin in enumerate(chunk_begins):
    chunks.append({
        "blob_id": blob_id,
        "chunk_index": i,
        "blob_chunk": blob[chunk_begin:chunk_begin + BLOB_CHUNK_SIZE]
    })
  return chunks