Use the operating system‘s spellchecker rather than Hunspell. This does not affect the “red underline” spellchecker which can consult Google’s server-based spellcheck service.
Use hunspell spellchecker rather than the operating system's spellchecker.
For most operating system except Windows, the decision to use the platform spellchecker or Hunspell spellchecker is made at build time. Therefore, use_browser_spellchecker and use_renderer_spellchecker are mutually exclusive for most operating systems except Windows.
For Windows OS, the decision to use the platform spellchecker or Hunspell spellchecker is made during runtime. Therefore, we include both build flags if the platform is Windows.
We also need to create the runtime feature flag kWinUseBrowserSpellChecker for Windows OS. The feature flag is used to choose between the platform or Hunspell spellchecker at runtime.
On Windows, the platform spell checker relies on user-installed language packs. It is possible for a user to enable spell checking in Chrome for a language while not having installed the necessary language pack in the Windows settings.
For those situations, the spell checker on Windows will first try to use the platform spell checker. For languages where this is not possible, Hunspell will be used instead.
To control this fallback logic, a separate build flag use_win_hybrid_spellchecker is used. In addition, for experiment purposes, a feature flag kWinUseHybridSpellChecker is used to control this behavior at runtime. Finally, this fallback logic requires the platform spell checker to be available, so it also uses the browser spell checker checks described above.
TODO(https://crbug.com/1000443): Use Windows preferred languages to help populate spellcheck settings.
Use union of Chromium preferred languages (from Language settings) and the Windows preferred languages (from system language settings) as the source of the spellcheck languages in the “Spell check” section of the Chromium language settings, provided they are supported for spellcheck.