Monitor add callback uniqueness.

Only allow the same instance of callback registered once in the
conditions monitor.

Test: atest ConditionMonitorTest#addCallback_withMultipleInstancesOfTheSameCallback_registerOnlyOne
Fix: 218921598
Change-Id: Ibbce271446e4039759e27bf889c4c672ac026c16

packages/SystemUI/src/com/android/systemui/util/condition/Monitor.java

@@ -145,6 +145,10 @@ public class Monitor implements CallbackController<Monitor.Callback> {
     }
 
     private void addCallbackLocked(@NotNull Callback callback) {
+        if (mCallbacks.contains(callback)) {
+            return;
+        }
+
         if (shouldLog()) Log.d(mTag, "adding callback");
         mCallbacks.add(callback);
 

packages/SystemUI/tests/src/com/android/systemui/util/condition/ConditionMonitorTest.java

@@ -194,6 +194,21 @@ public class ConditionMonitorTest extends SysuiTestCase {
         verify(callback).onConditionsChanged(true);
     }
 
+    @Test
+    public void addCallback_withMultipleInstancesOfTheSameCallback_registerOnlyOne() {
+        final Monitor monitor = new Monitor(mExecutor, new HashSet<>(), null /*callbacks*/);
+        final Monitor.Callback callback = mock(Monitor.Callback.class);
+
+        // Adds the same instance multiple times.
+        monitor.addCallback(callback);
+        monitor.addCallback(callback);
+        monitor.addCallback(callback);
+        mExecutor.runAllReady();
+
+        // Callback should only be triggered once.
+        verify(callback, times(1)).onConditionsChanged(true);
+    }
+
     @Test
     public void removeCallback_shouldNoLongerReceiveUpdate() {
         final Condition condition = mock(Condition.class);