DO NOT MERGE. Fix issue where back stack is not cleared when opening email from a notification.

Fixes b/5716835 back stack in email gets messed up in certain circumstances

Change-Id: I499a1c19f1ebbb7e4debde690cacf17f9f6c3454
diff --git a/src/com/android/email/NotificationController.java b/src/com/android/email/NotificationController.java
index 5ed3e01..991f3ba 100644
--- a/src/com/android/email/NotificationController.java
+++ b/src/com/android/email/NotificationController.java
@@ -443,7 +443,7 @@
         } else {
             intent = Welcome.createOpenMessageIntent(mContext, accountId, mailboxId, messageId);
         }
-
+        intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
         long now = mClock.getTime();
         boolean enableAudio = (now - mLastMessageNotifyTime) > MIN_SOUND_INTERVAL_MS;
         Notification notification = createAccountNotification(