chromeos: Improve comment for feature SplitSettingsSync

Better explain the feature, and note that the code may be enabled by a
field trial even though it defaults to disabled.

Bug: none
Change-Id: I6e596f1535f86128df67a8f38f715f0140208258
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2236494
Auto-Submit: James Cook <jamescook@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#776240}

chromeos/constants/chromeos_features.cc

@@ -359,9 +359,18 @@ const base::Feature kSmartDimNewMlAgent{"SmartDimNewMlAgent",
 const base::Feature kSmartDimModelV3{"SmartDimModelV3",
                                      base::FEATURE_DISABLED_BY_DEFAULT};
 
-// Enables separate sync controls for OS settings (display, keyboard, etc.).
-// For example, the user could choose to sync OS settings but not browser
-// settings.
+// This feature:
+// - Creates a new "Sync your settings" section in Chrome OS settings
+// - Moves app, wallpaper and Wi-Fi sync to OS settings
+// - Provides a separate toggle for OS preferences, distinct from browser
+//   preferences
+// - Makes the OS ModelTypes run in sync transport mode, controlled by a
+//   master pref for the OS sync feature
+// - Updates the OOBE sync consent screen
+//
+// NOTE: The feature is rolling out via a client-side Finch trial, so the actual
+// state will vary. See config in
+// chrome/browser/chromeos/sync/split_settings_sync_field_trial.cc
 const base::Feature kSplitSettingsSync{"SplitSettingsSync",
                                        base::FEATURE_DISABLED_BY_DEFAULT};