fix(alert_tab): fix broken alert history

public/app/features/alerting/alert_tab_ctrl.ts

@@ -106,6 +106,13 @@ export class AlertTabCtrl {
     }));
   }
 
+  changeTabIndex(newTabIndex) {
+    this.subTabIndex = newTabIndex;
+
+    if (this.subTabIndex === 2) {
+      this.getAlertHistory();
+    }
+  }
 
   notificationAdded() {
     var model = _.findWhere(this.notifications, {name: this.addNotificationSegment.value});

public/app/features/alerting/partials/alert_tab.html

@@ -2,15 +2,15 @@
 	<aside class="edit-sidemenu-aside">
 		<ul class="edit-sidemenu">
 			<li ng-class="{active: ctrl.subTabIndex === 0}">
-				<a ng-click="ctrl.subTabIndex = 0">Alert Config</a>
+				<a ng-click="ctrl.changeTabIndex(0)">Alert Config</a>
 			</li>
 			<li ng-class="{active: ctrl.subTabIndex === 1}">
-				<a ng-click="ctrl.subTabIndex = 1">
+				<a ng-click="ctrl.changeTabIndex(1)">
 					Notifications <span class="muted">({{ctrl.alert.notifications.length}})</span>
 				</a>
 			</li>
 			<li ng-class="{active: ctrl.subTabIndex === 2}">
-				<a ng-click="ctrl.subTabIndex = 2">Alert History</a>
+				<a ng-click="ctrl.changeTabIndex(2)">Alert History</a>
 			</li>
       <li>
 				<a ng-click="ctrl.delete()">Delete</a>