Add it-IT to kSupportedSpellCheckerLanguages

This CL adds one more language to kSupportedSpellCheckerLanguages.

This makes it so that all region/dictionary values in
kSupportedSpellCheckerLanguages that are also in kAcceptLanguageList
have their own entry in kSupportedSpellCheckerLanguages and prevents
duplicate overflow values for languages in kAcceptLanguageList.

Bug: 1074284
Change-Id: Id99ef28e99367672a92c14d2dbfa7eeb23ceaf19
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2625588Reviewed-by: Josh Simmons <jds@google.com>
Commit-Queue: Josh Simmons <jds@google.com>
Auto-Submit: Trevor  Perrier <perrier@chromium.org>
Cr-Commit-Position: refs/heads/master@{#842811}

components/spellcheck/common/spellcheck_common.cc

@@ -62,6 +62,7 @@ static constexpr LanguageRegion kSupportedSpellCheckerLanguages[] = {
     {"hy", "hy"},
     {"id", "id-ID"},
     {"it", "it-IT"},
+    {"it-IT", "it-IT"},
     {"ko", "ko"},
     {"lt", "lt-LT"},
     {"lv", "lv-LV"},