sparse_img.py: Divide NONZERO blocks into groups.

    nonzero_blocks = []

    reference = '\0' * self.blocksize

    # Workaround for bug 23227672. For squashfs, we don't have a system.map. So

    # the whole system image will be treated as a single file. But for some

    # unknown bug, the updater will be killed due to OOM when writing back the

    # patched image to flash (observed on lenok-userdebug MEA49). Prior to

    # getting a real fix, we evenly divide the non-zero blocks into smaller

    # groups (currently 1024 blocks or 4MB per group).

    # Bug: 23227672

    MAX_BLOCKS_PER_GROUP = 1024

    nonzero_groups = []

    f = self.simg_f

    for s, e in remaining:

      for b in range(s, e):

          nonzero_blocks.append(b)

          nonzero_blocks.append(b+1)

    assert zero_blocks or nonzero_blocks or clobbered_blocks

          if len(nonzero_blocks) >= MAX_BLOCKS_PER_GROUP:

            nonzero_groups.append(nonzero_blocks)

            # Clear the list.

            nonzero_blocks = []

    if nonzero_blocks:

      nonzero_groups.append(nonzero_blocks)

      nonzero_blocks = []

    assert zero_blocks or nonzero_groups or clobbered_blocks

    if zero_blocks:

      out["__ZERO"] = rangelib.RangeSet(data=zero_blocks)

    if nonzero_blocks:

      out["__NONZERO"] = rangelib.RangeSet(data=nonzero_blocks)

    if nonzero_groups:

      for i, blocks in enumerate(nonzero_groups):

        out["__NONZERO-%d" % i] = rangelib.RangeSet(data=blocks)

    if clobbered_blocks:

      out["__COPY"] = clobbered_blocks