GitLab

This CL applying multiple change to fix the way ItemizeTextToRuns
split a sequence of codepoints into runs with same/compatible
scripts.

 *) Increase kMaxScripts to support codepoints with large amount of scripts.
    Some codepoint has much more than the previous maximum 5 scripts
    (see indic_fraction test u+A830, dev_danda u+0964).

 *) Only rely on Script extensions to find longest script interval
    see: http://www.unicode.org/reports/tr24/tr24-29.html
    (more specifically Table 7. Script_Extensions Examples)

    Cases where script was 'Common' and Script Extensions has a set of
    explicit script was not handled properly.

                 Script       Script Extensions     Results
     Previously: Common       {Hira Kana}       ->  {Hira Kana Common}
     Currently:  Common       {Hira Kana}       ->  {Hira Kana}

    This mistake has the consequene to put lot of codepoints from different
    scripts into the same bucket ('common') and there won't be a font that
    can renders (too) different scripts. Which is causing expensive fallback
    fonts lookups.

    ""
      U+30FC  Scx = {Hira Kana}  Script = Common

      Example 1. Mixed script detection for spoofing.
      Using the Script property alone, for example, will not detect that the U+30FC
      KATAKANA-HIRAGANA PROLONGED SOUND MARK (Script=Common) should not be mixed with
      Latin.
    ""

  *) Inherited script should only be applied to the previous codepoint.
     It was incorrectly intersected with the previous or the next one.

[ RUN      ] ItemizeTextToRunsScripts/RenderTextTestWithRunListCase.ItemizeTextToRuns/diac_lat
../../ui/gfx/render_text_unittest.cc(930): error: Expected equality of these values:
  param.expected
    Which is: "[0][1->2]"
  GetRunListStructureString()
    Which is: "[0->2]"

    That was causing more codepoints to be appended to long sequence of script
    when type was 'Common'.


Bug: 1017194
Change-Id: Ia1339697a44d0d7bbac389997e9fa2878e6eac1d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1876489Reviewed-by: Robert Liao <robliao@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Commit-Queue: Etienne Bergeron <etienneb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710416}