languageSettingsPrivate API definition and stub implementation

The IDL was approved by API review and got l-g-t-m from kalman@ at https://codereview.chromium.org/1102693002/

This IDL is the same, modulo stevenjb's comments on that CL and some bug fixes.

BUG=479043

[email protected],[email protected],[email protected]
[email protected]

kalman:
  chrome/common/extensions/api/_api_features.json
  chrome/common/extensions/api/language_settings_private.idl (rubberstamped in 1102693002)
  chrome/common/extensions/api/schemas.gypi

asvitkine:
  extensions/browser/extension_function_histogram_value.h
  tools/metrics/histograms/histograms.xml

dbeam:
  (generated file: third_party/closure_compiler/externs/language_settings_private.js)

Review URL: https://codereview.chromium.org/1155093006

Cr-Commit-Position: refs/heads/master@{#338632}
diff --git a/extensions/browser/extension_function_histogram_value.h b/extensions/browser/extension_function_histogram_value.h
index 5b5f82b..81b36c51 100644
--- a/extensions/browser/extension_function_histogram_value.h
+++ b/extensions/browser/extension_function_histogram_value.h
@@ -1121,6 +1121,14 @@
   FILEMANAGERPRIVATEINTERNAL_GETENTRYACTIONS,
   FILEMANAGERPRIVATEINTERNAL_EXECUTEENTRYACTION,
   MDNS_FORCEDISCOVERY,
+  LANGUAGESETTINGSPRIVATE_GETLANGUAGELIST,
+  LANGUAGESETTINGSPRIVATE_SETLANGUAGELIST,
+  LANGUAGESETTINGSPRIVATE_GETSPELLCHECKDICTIONARYSTATUS,
+  LANGUAGESETTINGSPRIVATE_GETSPELLCHECKWORDS,
+  LANGUAGESETTINGSPRIVATE_GETTRANSLATETARGETLANGUAGE,
+  LANGUAGESETTINGSPRIVATE_GETINPUTMETHODLISTS,
+  LANGUAGESETTINGSPRIVATE_ADDINPUTMETHOD,
+  LANGUAGESETTINGSPRIVATE_REMOVEINPUTMETHOD,
   // Last entry: Add new entries above, then run:
   // python tools/metrics/histograms/update_extension_histograms.py
   ENUM_BOUNDARY