Update slot's m_distributedIndices correctly

This CL fixes a bug in https://codereview.chromium.org/1611413005.

In HTMLSlotElement::appendDistributedFrom, we should use other.m_distributedNodes, instead of other.m_distributedIndices,
to update this slot's m_distributedIndices correctly.

BUG=531990

Review URL: https://codereview.chromium.org/1695243005

Cr-Commit-Position: refs/heads/master@{#375824}
1 file changed