GitLab

When a run ended in a grapheme cluster consisting of a least two
characters, and this grapheme resulted in not being shaped with the
current font and needed fallback, then the full run from the beginning
was incorrectly rendered in the fallback font. This is because one state
transition between shaped and not shaped was not recognized, as the
last_change_position had been advanced too far.

To fix this, I clarified the shaping loop and moved the logic for
commiting glyphs and queueing characters for reshaping into separate
functions. When reaching the end of the glyph run, transitions between
shaped or unshaped are detected for the last grapheme cluster and added
to the ShapeResult or the reshaping queue accordingly.

       inspector-protocol/layout-fonts/prefix-fallback-multi-character-grapheme.js
       svg/text/combining-character-queries-expected.svg

Bug: 758380
Tests: EmojiZWJSequence in HarfBuzzShaperTest.cpp,
Change-Id: I95d536c488ac602cb4bdfd4e1ac4a729f92b1462
Reviewed-on: https://chromium-review.googlesource.com/657977
Commit-Queue: Dominik Röttsches <drott@chromium.org>
Reviewed-by: Emil A Eklund <eae@chromium.org>
Cr-Commit-Position: refs/heads/master@{#504327}