Eliminate next-alarm-clock broadcast flapping

When multiple alarm clocks are scheduled at the same time, we would
flap among the alternatives for considering them the 'next upcoming
alarm clock', which in turn would generate [many] spurious broadcasts
about changes to the upcoming alarm situation.  This is now fixed;
once we have found the soonest upcoming alarm clock, we stick with
that one until it becomes unavailable, eliminating the spurious
broadcast traffic.

Bug 29501073

Change-Id: Ice1892490bb339e05fa8bd9d324fa1c6718b4942
(cherry picked from commit 76389c00d3d3ce79e48d9e87b597707ed3e8970c)
(cherry picked from commit c60da1edc1f5f8d028c3e88b8ca51d790f2a012a)
diff --git a/services/core/java/com/android/server/AlarmManagerService.java b/services/core/java/com/android/server/AlarmManagerService.java
index 312553a..3f59b02 100644
--- a/services/core/java/com/android/server/AlarmManagerService.java
+++ b/services/core/java/com/android/server/AlarmManagerService.java
@@ -1732,9 +1732,10 @@
                 Alarm a = alarms.get(j);
                 if (a.alarmClock != null) {
                     final int userId = UserHandle.getUserId(a.uid);
+                    AlarmManager.AlarmClockInfo current = mNextAlarmClockForUser.get(userId);
 
                     if (DEBUG_ALARM_CLOCK) {
-                        Log.v(TAG, "Found AlarmClockInfo at " +
+                        Log.v(TAG, "Found AlarmClockInfo " + a.alarmClock + " at " +
                                 formatNextAlarm(getContext(), a.alarmClock, userId) +
                                 " for user " + userId);
                     }
@@ -1742,6 +1743,10 @@
                     // Alarms and batches are sorted by time, no need to compare times here.
                     if (nextForUser.get(userId) == null) {
                         nextForUser.put(userId, a.alarmClock);
+                    } else if (a.alarmClock.equals(current)
+                            && current.getTriggerTime() <= nextForUser.get(userId).getTriggerTime()) {
+                        // same/earlier time and it's the one we cited before, so stick with it
+                        nextForUser.put(userId, current);
                     }
                 }
             }