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This patch implements break-after-space style line breaking. This style
is needed for 'white-space:pre-wrap', and when in editing.

The current layout engine handles this in BreakingContext. This patch
implements the style in LazyTextBreakIterator so that ShapingLineBreaker
can implement the behavior without additional code.

The current layout engine supports 3 modes:
1. break-before-space (most cases)
2. break-after-space (white-space:pre-wrap)
3. break-after-space + hanging space (editing)

This patch does not support 3rd mode yet, and that editing behavior is
slightly different from the current layout engine, closer to Edge. The
editing test failure is caused by this difference. I'll evaluate the
impact and the needs of the 3rd mode later.

There are more tests that actually pass, but they fail for other
reasons, such as the lack of quirks mode support.

BUG=636993

Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_layout_ng
Change-Id: Iec1b684da4dcf45f10eaa408889ebf77d387e668
Reviewed-on: https://chromium-review.googlesource.com/574903
Commit-Queue: Koji Ishii <kojii@chromium.org>
Reviewed-by: Emil A Eklund <eae@chromium.org>
Cr-Commit-Position: refs/heads/master@{#488169}