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This reverts commit 55549387.

Reason for revert: breaks gfx_unittests on (none) GPU on Mac
FallbackFontCommonScript/RenderTextTestWithFallbackFontCase.FallbackFont/common21
Expected equality of these values:
  missing_glyphs
    Which is: 1
  0

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

TBR=robliao@chromium.org,asvitkine@chromium.org,etienneb@chromium.org

Change-Id: I6ea8c752e40ed07522d0d336ada289934c899477
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1900433Reviewed-by: Joshua Pawlicki <waffles@chromium.org>
Commit-Queue: Joshua Pawlicki <waffles@chromium.org>
Cr-Commit-Position: refs/heads/master@{#712778}