Add cross-platform Force Dark variants to about://flags.

Cross-platform access to "forced dark mode" and its
config options is currently available via the --blink-settings flag.
This change simply provides easy access to specific sets of config
options for testing.

Bug: 985961
Change-Id: I733c2e7b896e8a5d5fffc1b9d783473db4056c9a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1721002
Commit-Queue: Aran Gilman <[email protected]>
Reviewed-by: Elly Fong-Jones <[email protected]>
Reviewed-by: Daniel Cheng <[email protected]>
Cr-Commit-Position: refs/heads/master@{#683691}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index 650c7beb..7031feb 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -918,6 +918,9 @@
 extern const char kPasswordImportName[];
 extern const char kPasswordImportDescription[];
 
+extern const char kForceWebContentsDarkModeName[];
+extern const char kForceWebContentsDarkModeDescription[];
+
 extern const char kPeriodicBackgroundSyncName[];
 extern const char kPeriodicBackgroundSyncDescription[];
 
@@ -1264,9 +1267,6 @@
 extern const char kAndroidSurfaceControl[];
 extern const char kAndroidSurfaceControlDescription[];
 
-extern const char kAndroidWebContentsDarkMode[];
-extern const char kAndroidWebContentsDarkModeDescription[];
-
 extern const char kAppNotificationStatusMessagingName[];
 extern const char kAppNotificationStatusMessagingDescription[];