Make getNumObservers @VisibleForTesting so that it can be tested outside of package org.webrtc

Bug: webrtc:0
Change-Id: I66259bba8c724889df3ee22a8d6b9710a04ba671
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/361863
Reviewed-by: Jonas Oreland <jonaso@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Jonas Oreland <jonaso@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#42973}
diff --git a/sdk/android/api/org/webrtc/NetworkMonitor.java b/sdk/android/api/org/webrtc/NetworkMonitor.java
index ca7e4d5..428463c 100644
--- a/sdk/android/api/org/webrtc/NetworkMonitor.java
+++ b/sdk/android/api/org/webrtc/NetworkMonitor.java
@@ -13,10 +13,12 @@
 import android.content.Context;
 import android.os.Build;
 import androidx.annotation.Nullable;
+import androidx.annotation.VisibleForTesting;
 import java.util.ArrayList;
 import java.util.List;
 import org.webrtc.NetworkChangeDetector;
 
+
 /**
  * Borrowed from Chromium's
  * src/net/android/java/src/org/chromium/net/NetworkChangeNotifier.java
@@ -349,7 +351,8 @@
   }
 
   // For testing only.
-  int getNumObservers() {
+  @VisibleForTesting
+  public int getNumObservers() {
     synchronized (networkChangeDetectorLock) {
       return numObservers;
     }