Clean up: Removed synchronized on mHandler

* Cleaned up synchronized on mHandler in both startDelayedWrite and tests
* This was not needed as startDelayedWrite as a synchronized at the method level
* Limited access level to mHandler and startDelayedWrite now that tests don't access this anymore directly.

Author: jkasten2

OneSignalSDK/onesignal/src/main/java/com/onesignal/OneSignalPrefs.java

@@ -123,7 +123,7 @@ class OneSignalPrefs {
     }
 
     public static class WritePrefHandlerThread extends HandlerThread {
-        public Handler mHandler;
+        private Handler mHandler;
 
         private static final int WRITE_CALL_DELAY_TO_BUFFER_MS = 200;
         private long lastSyncTime = 0L;
@@ -132,7 +132,7 @@ public static class WritePrefHandlerThread extends HandlerThread {
             super(name);
         }
 
-        synchronized void startDelayedWrite() {
+        private synchronized void startDelayedWrite() {
             // A Context is required to write,
             //   if not available now later OneSignal.setContext will call this again.
             if (OneSignal.appContext == null)
@@ -143,15 +143,12 @@ synchronized void startDelayedWrite() {
                 mHandler = new Handler(getLooper());
             }
 
-            synchronized (mHandler) {
-                mHandler.removeCallbacksAndMessages(null);
-                if (lastSyncTime == 0)
-                    lastSyncTime = System.currentTimeMillis();
+            mHandler.removeCallbacksAndMessages(null);
+            if (lastSyncTime == 0)
+                lastSyncTime = System.currentTimeMillis();
 
-                long delay = lastSyncTime - System.currentTimeMillis() + WRITE_CALL_DELAY_TO_BUFFER_MS;
-
-                mHandler.postDelayed(getNewRunnable(), delay);
-            }
+            long delay = lastSyncTime - System.currentTimeMillis() + WRITE_CALL_DELAY_TO_BUFFER_MS;
+            mHandler.postDelayed(getNewRunnable(), delay);
         }
 
         /**

OneSignalSDK/unittest/src/test/java/com/test/onesignal/TestHelpers.java

@@ -130,15 +130,10 @@ static void stopAllOSThreads() {
    static void flushBufferedSharedPrefs() {
       OneSignalPrefs.WritePrefHandlerThread handlerThread = OneSignalPackagePrivateHelper.OneSignalPrefs.prefsHandler;
 
-      if (handlerThread.mHandler == null)
+      if (handlerThread.getLooper() == null)
          return;
-
-      synchronized (handlerThread.mHandler) {
-         if (handlerThread.getLooper() == null)
-            return;
-         Scheduler scheduler = shadowOf(handlerThread.getLooper()).getScheduler();
-         while (scheduler.runOneTask());
-      }
+      Scheduler scheduler = shadowOf(handlerThread.getLooper()).getScheduler();
+      while (scheduler.runOneTask());
    }
 
    // Join all OS_ threads