Message Center: Add flag to chrome://flags for enabling redesigned stacking bar UI.

BUG=921250

Change-Id: I09ebc0d4d3acc931d5d3ad28152f5040c83bfca6
Reviewed-on: https://chromium-review.googlesource.com/c/1492834
Commit-Queue: Tim Song <tengs@chromium.org>
Reviewed-by: Tetsui Ohkubo <tetsui@chromium.org>
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#636682}
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index b529f7c..ecb6d13 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -4122,6 +4122,13 @@
      flag_descriptions::kAutofillShowFullDisclosureLabelDescription, kOsAll,
      FEATURE_VALUE_TYPE(autofill::features::kAutofillShowFullDisclosureLabel)},
 
+#if defined(OS_CHROMEOS)
+    {"ash-notification-stacking-bar-redesign",
+     flag_descriptions::kAshNotificationStackingBarRedesignName,
+     flag_descriptions::kAshNotificationStackingBarRedesignDescription, kOsCrOS,
+     FEATURE_VALUE_TYPE(ash::features::kNotificationStackingBarRedesign)},
+#endif  // OS_CHROMEOS
+
     // NOTE: Adding a new flag requires adding a corresponding entry to enum
     // "LoginCustomFlags" in tools/metrics/histograms/enums.xml. See "Flag
     // Histograms" in tools/metrics/histograms/README.md (run the
diff --git a/chrome/browser/flag-metadata.json b/chrome/browser/flag-metadata.json
index 51c8515..d0cc05d 100644
--- a/chrome/browser/flag-metadata.json
+++ b/chrome/browser/flag-metadata.json
@@ -172,6 +172,11 @@
     "expiry_milestone": -1
   },
   {
+    "name": "ash-notification-stacking-bar-redesign",
+    "owners": [ "tengs" ],
+    "expiry_milestone": 75
+  },
+  {
     "name": "ash-shelf-color",
     // "owners": [ "your-team" ],
     "expiry_milestone": 76
diff --git a/chrome/browser/flag_descriptions.cc b/chrome/browser/flag_descriptions.cc
index 37bac18..0ebc5b7 100644
--- a/chrome/browser/flag_descriptions.cc
+++ b/chrome/browser/flag_descriptions.cc
@@ -3489,6 +3489,12 @@
     "Enable Zero State App Reinstall Suggestions feature in launcher, which "
     "will show app reinstall recommendations at end of zero state list.";
 
+extern const char kAshNotificationStackingBarRedesignName[] =
+    "Redesigned notification stacking bar";
+extern const char kAshNotificationStackingBarRedesignDescription[] =
+    "Enables the redesigned notification stacking bar UI with a \"Clear all\" "
+    "button.";
+
 #endif  // defined(OS_CHROMEOS)
 
 // Random platform combinations -----------------------------------------------
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index d3ce0e5..89e0a175 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -2082,6 +2082,9 @@
 extern const char kEnableAppReinstallZeroStateName[];
 extern const char kEnableAppReinstallZeroStateDescription[];
 
+extern const char kAshNotificationStackingBarRedesignName[];
+extern const char kAshNotificationStackingBarRedesignDescription[];
+
 #endif  // #if defined(OS_CHROMEOS)
 
 // Random platform combinations -----------------------------------------------
diff --git a/tools/metrics/histograms/enums.xml b/tools/metrics/histograms/enums.xml
index ae7e835..2b8e3e7 100644
--- a/tools/metrics/histograms/enums.xml
+++ b/tools/metrics/histograms/enums.xml
@@ -31487,6 +31487,7 @@
   <int value="-1112782121" label="AndroidSigninPromos:disabled"/>
   <int value="-1107762575" label="enable-data-reduction-proxy-config-client"/>
   <int value="-1107103335" label="FsNosymfollow:enabled"/>
+  <int value="-1103099187" label="NotificationStackingBarRedesign:disabled"/>
   <int value="-1102212525" label="enable-tcp-fastopen"/>
   <int value="-1099142083" label="V8Ignition:disabled"/>
   <int value="-1099135056" label="AsyncDns:enabled"/>
@@ -32308,6 +32309,7 @@
   <int value="331770879" label="CrostiniAppSearch:disabled"/>
   <int value="332391072" label="cs-contextual-cards-bar-integration"/>
   <int value="334802038" label="OfflinePreviews:disabled"/>
+  <int value="335976733" label="NotificationStackingBarRedesign:enabled"/>
   <int value="336429189" label="DisallowUnsafeHttpDownloads:disabled"/>
   <int value="339671131" label="disable-per-user-timezone"/>
   <int value="341152650" label="SoundContentSetting:enabled"/>