[line-clamp] Support truncating line-clamp: auto inside a nested block

[chromium-wpt-export-bot]

Our previous patch, https://crrev.com/c/5490736, implemented
line-clamp: auto, which clamps a line-clamp container based on its
height constraints. However, that patch only worked when the clamp
point is directly inside the line-clamp container (or its
InlineNode), rather than inside a nested block.

Clamping by height inside nested blocks adds some challenges, which we
resolve in this CL:

• The bottom padding, border and margin need to be taken into
  account, since they mean the BFC offset at which the content of a
  block container clamps might be different from the parent's BFC
  offset. We fixed this by updating the clamp BFC offset for every
  block descendant according to their bottom padding and border. We
  leave margins for a follow-up CL.

• previous_inflow_position->logical_block_offset was previously
  used as both the intrinsic size so far of the current block
  container after a child layout, and the BFC offset after the
  laid out child. These are only the same if the block box
  establishes a new BFC (i.e. is the line-clamp container). This CL
  passes BlockLineClampData::UpdateAfterLayout the block box's
  BFC offset, which solves this issue.

• Since every block box which contains the clamp point needs to have
  its intrinsic size set depending on the clamp point, it is
  possible for a block box to change its intrinsic size such that,
  as far as the parent is concerned, the BFC offset has not yet been
  reached. To avoid this, we add a HasContentAfterLineClamp method
  to LayoutResult, and pass the child's LayoutResult* to
  BlockLineClampData::UpdateAfterLayout.

Bug: 40336192
Change-Id: Ied3cb5f60460d4746a4ce13b4684d623adf0ddcd
Reviewed-on: https://chromium-review.googlesource.com/5547983
WPT-Export-Revision: 145c33f3d5123cf43d994043cba1ad619b74b4a2