If a block container has box-decoration-break:clone, its block-end border and
padding (BP) are *usually* drawn at the block-end edge of the current
column/page. Thus, when computing the available block-size for its children, we
should subtract its block-end border BP from it.
When I claim the block-end BP are *usually* drawn at the block-end edge of the
column/page, the exception is when a block container with a definite block-size
runs out of its block-size in a column/page. In this case, the block-end BP is
drawn at the block-end edge of its content-box. This patch wires the effective
content-box block-size computed in nsBlockFrame::Reflow() into
BlockReflowInput's constructor, and we do not subtract its block-end border BP
from the `mContentArea.BSize(wm)` when this case happens.
`BlockReflowInput::ContentBSize()` is the correct available block-size to reflow
the children, precomputed in BlockReflowInput's constructor. See
https://searchfox.org/mozilla-central/rev/c12a59323ee46b29b90c9917a3a7a70ea714ffec/layout/generic/BlockReflowInput.cpp#118-126
The remove hunk was a hack, working only for ColumnSetWrapper with
`box-decoration-break:clone`. It's no longer needed.
Differential Revision: https://phabricator.services.mozilla.com/D138367
476a867c3b
