personalization: add flag kScreenSaverDuration

Feature flag for screen saver duration settings.

BUG=b:274173927
TEST=unit_tests --gtest_filter='AboutFlagsHistogramTest.*'

Change-Id: I8fdd61b283f483c5383c45c3b0e9cf330d97b490
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4355091
Reviewed-by: Jason Thai <[email protected]>
Commit-Queue: Jerry Liu <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1119586}
diff --git a/chrome/browser/flag_descriptions.cc b/chrome/browser/flag_descriptions.cc
index 2384d91..4bd7f402 100644
--- a/chrome/browser/flag_descriptions.cc
+++ b/chrome/browser/flag_descriptions.cc
@@ -2769,6 +2769,10 @@
     "behavior. Please file bugs at https://bugs.chromium.org/p/chromium/issues/"
     "entry?labels=StoragePartitioning-trial-bugs&components=Blink%3EStorage.";
 
+const char kScreenSaverDurationName[] = "Screen saver duration settings";
+const char kScreenSaverDurationDescription[] =
+    "Allow users to customize screen saver running time.";
+
 const char kScreenSaverPreviewName[] = "Screen saver preview";
 const char kScreenSaverPreviewDescription[] =
     "Enables the screen saver preview feature which allows the users to "