Added flag to notification expansion animation

Added a cli flag as well as a gui flag for notification expansion
animation on chrome side.

Test: Manually tested animations after turning on/off the flag.
Bug: b/117914707
Change-Id: Ib388661bcc1da1d41bb86e4976c2a3ea4ba8195a
Reviewed-on: https://chromium-review.googlesource.com/c/1297774
Reviewed-by: Xiyuan Xia <[email protected]>
Reviewed-by: Greg Kerr <[email protected]>
Reviewed-by: Hidehiko Abe <[email protected]>
Reviewed-by: Yoshiki Iguchi <[email protected]>
Reviewed-by: Tetsui Ohkubo <[email protected]>
Commit-Queue: Mitsuru Otsuka <[email protected]>
Cr-Commit-Position: refs/heads/master@{#603402}
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index ab18b621..9e71fdb 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -4435,6 +4435,15 @@
     {"enable-send-tab-to-self", flag_descriptions::kSendTabToSelfName,
      flag_descriptions::kSendTabToSelfDescription, kOsAll,
      FEATURE_VALUE_TYPE(features::kSendTabToSelf)},
+
+#if defined(OS_CHROMEOS)
+    {"ash-enable-notification-expansion-animation",
+     flag_descriptions::kEnableNotificationExpansionAnimationName,
+     flag_descriptions::kEnableNotificationExpansionAnimationDescription,
+     kOsCrOS,
+     FEATURE_VALUE_TYPE(ash::features::kNotificationExpansionAnimation)},
+
+#endif  // defined(OS_CHROMEOS)
 };
 
 class FlagsStateSingleton {