Improve exception stack traces in OptimizedMessageNotifier.

app/src/main/java/org/thoughtcrime/securesms/util/Util.java

@@ -627,4 +627,25 @@ public class Util {
       return false;
     }
   }
+
+  /**
+   * Appends the stack trace of the provided throwable onto the provided primary exception. This is
+   * useful for when exceptions are thrown inside of asynchronous systems (like runnables in an
+   * executor) where you'd otherwise lose important parts of the stack trace. This lets you save a
+   * throwable at the entry point, and then combine it with any caught exceptions later.
+   *
+   * @return The provided primary exception, for convenience.
+   */
+  public static RuntimeException appendStackTrace(@NonNull RuntimeException primary, @NonNull Throwable secondary) {
+    StackTraceElement[] now      = primary.getStackTrace();
+    StackTraceElement[] then     = secondary.getStackTrace();
+    StackTraceElement[] combined = new StackTraceElement[now.length + then.length];
+
+    System.arraycopy(now, 0, combined, 0, now.length);
+    System.arraycopy(then, 0, combined, now.length, then.length);
+
+    primary.setStackTrace(combined);
+
+    return primary;
+  }
 }