QuietNotificationPrompts feature enabled by default

The feature has all the necessary approvals, and it was running as an
experiment for 1% in stable. Next experimental phase, enables one or
more parameters for 98% of the users in stable, and requires the feature
to be enabled by default.

Bug: 1005015
Change-Id: I0e6d20635d0dc65b59eecbba0c0f067eac638187
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2080270Reviewed-by: Balazs Engedy <engedy@chromium.org>
Commit-Queue: Balazs Engedy <engedy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#747650}

chrome/common/chrome_features.cc

@@ -601,8 +601,8 @@ const base::Feature kPushMessagingBackgroundMode{
     "PushMessagingBackgroundMode", base::FEATURE_DISABLED_BY_DEFAULT};
 
 // Enables using quiet prompts for notification permission requests.
-const base::Feature kQuietNotificationPrompts{
-    "QuietNotificationPrompts", base::FEATURE_DISABLED_BY_DEFAULT};
+const base::Feature kQuietNotificationPrompts{"QuietNotificationPrompts",
+                                              base::FEATURE_ENABLED_BY_DEFAULT};
 
 #if defined(OS_CHROMEOS)
 // Enables permanent removal of Legacy Supervised Users on startup.