GitLab

This is a reland of 55549387

Original change's description:
> Fix RenderText itemization for complex emoji
> 
> 
> 
> This CL is a refactoring on the way RenderText do
> 
> ItemizeTextToRuns for the corner cases where a run
> 
> should be split in grapheme clusters.
> 
> 
> 
> The previous code was naming these cases:
> 
>   * Unusual characters
> 
>   * Special characters
> 
>   * Non-regular characters
> 
> But they should be more specific on the purpose of splitting the runs.
> 
> 
> 
> Also, the algorithm used for splitting a sequence of codepoint
> 
> was based on the code block of the corresponding codepoints
> 
> and few cases where trying to merge adjacent codepoint in
> 
> a grapheme. The algorithm was incorrect multiple cases (e.g. emoji).
> 
> 
> 
> Unicode provide a way to split a sequence of codepoints into
> 
> grapheme and grapheme clusters.
> 
> They provide a state machine which is using the codepoint proporties
> 
> to decide if the current location is a grapheme boundaries.
> 
> 
> 
> The ICU library is providing an API over the character properties
> 
> to help iterating over graphemes.
> 
>   * ubrk_open
> 
>   * ubrk_first
> 
>   * ubrk_next
> 
>   * ubrk_close
> 
> 
> 
> The class base::i18n::BreakIterator(..., BREAK_CHARACTER) is
> 
> providing an easy to use wrapper over that API.
> 
> 
> 
> 
> 
> The current CL is replacing the previous characters based splitting
> 
> algorithm by the graphemes based version.
> 
> 
> 
> 
> 
> 
> 
> See emoji sequence:
> 
>   http://www.unicode.org/reports/tr51/
> 
>   1.4.5 Emoji Sequences
> 
> 
> 
> The full emoji list:
> 
>   * http://unicode.org/emoji/charts/full-emoji-list.html
> 
> Emoji data, used to make our unittests:
> 
>   * http://www.unicode.org/Public/emoji/12.0/emoji-data.txt
> 
> 
> 
> 
> see: UNICODE TEXT SEGMENTATION (http://unicode.org/reports/tr29/)
> 
> see: https://cs.chromium.org/chromium/src/third_party/icu/source/common/unicode/ubrk.h
> 
> see: https://cs.chromium.org/chromium/src/base/i18n/break_iterator.h
> 
> Change-Id: I6b9a9c79021f2ce0e2db7cdefdd0838b5911f445
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1788804
> Commit-Queue: Etienne Bergeron <etienneb@chromium.org>
> Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
> Reviewed-by: Robert Liao <robliao@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#712704}

Change-Id: I64c877907d6e961bd223a7c4cb1193c240b0b7ac
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1900347Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Commit-Queue: Etienne Bergeron <etienneb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#713179}