Fix color for low battery warning notification

Bug: 1159169
Change-Id: I9a23bed470b544d5da3938a6889b28fd2375201c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2643700Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Ahmed Mehfooz <amehfooz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#845829}

ash/system/power/battery_notification.cc

@@ -52,7 +52,7 @@ message_center::SystemNotificationWarningLevel GetWarningLevelMD(
     return message_center::SystemNotificationWarningLevel::NORMAL;
   } else if (notification_state ==
              PowerNotificationController::NOTIFICATION_LOW_POWER) {
-    return message_center::SystemNotificationWarningLevel::NORMAL;
+    return message_center::SystemNotificationWarningLevel::WARNING;
   } else if (notification_state ==
              PowerNotificationController::NOTIFICATION_CRITICAL) {
     return message_center::SystemNotificationWarningLevel::CRITICAL_WARNING;