Add logs to detect negative changes in system clock.

app/src/main/java/org/thoughtcrime/securesms/ApplicationContext.java

@@ -231,6 +231,16 @@ public class ApplicationContext extends MultiDexApplication implements AppForegr
       KeyCachingService.onAppForegrounded(this);
       ApplicationDependencies.getShakeToReport().enable();
       checkBuildExpiration();
+
+      long lastForegroundTime = SignalStore.misc().getLastForegroundTime();
+      long currentTime        = System.currentTimeMillis();
+      long timeDiff           = currentTime - lastForegroundTime;
+
+      if (timeDiff < 0) {
+        Log.w(TAG, "Time travel! The system clock has moved backwards. (currentTime: " + currentTime + " ms, lastForegroundTime: " + lastForegroundTime + " ms, diff: " + timeDiff + " ms)");
+      }
+
+      SignalStore.misc().setLastForegroundTime(currentTime);
     });
 
     Log.d(TAG, "onStart() took " + (System.currentTimeMillis() - startTime) + " ms");

app/src/main/java/org/thoughtcrime/securesms/keyvalue/MiscellaneousValues.java

@@ -25,6 +25,7 @@ public final class MiscellaneousValues extends SignalStoreValues {
   private static final String LAST_GV2_PROFILE_CHECK_TIME     = "misc.last_gv2_profile_check_time";
   private static final String CDS_TOKEN                       = "misc.cds_token";
   private static final String LAST_FCM_FOREGROUND_TIME        = "misc.last_fcm_foreground_time";
+  private static final String LAST_FOREGROUND_TIME            = "misc.last_foreground_time";
 
   MiscellaneousValues(@NonNull KeyValueStore store) {
     super(store);
@@ -175,4 +176,12 @@ public final class MiscellaneousValues extends SignalStoreValues {
   public void setLastFcmForegroundServiceTime(long time) {
     putLong(LAST_FCM_FOREGROUND_TIME, time);
   }
+
+  public long getLastForegroundTime() {
+    return getLong(LAST_FOREGROUND_TIME, 0);
+  }
+
+  public void setLastForegroundTime(long time) {
+    putLong(LAST_FOREGROUND_TIME, time);
+  }
 }