Fix comment in dark mode feature.

We don't want to require the feature to be on when *forcing*
dark mode.

Bug: 850098

Change-Id: Ie6a7f8e7a34e1436136664cf08db2015e69a790e
Reviewed-on: https://chromium-review.googlesource.com/1254862Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Leonard Grey <lgrey@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595532}

ui/base/ui_base_features.h

@@ -83,7 +83,7 @@ UI_BASE_EXPORT extern const base::Feature kEnableOzoneDrmMojo;
 UI_BASE_EXPORT bool IsOzoneDrmMojo();
 
 // Whether default UI should use a dark mode color scheme, if enabled on
-// macOS Mojave/Windows 10, or the --force-dark-mode flag is provided.
+// macOS Mojave/Windows 10.
 UI_BASE_EXPORT extern const base::Feature kDarkMode;
 
 }  // namespace features