Track previously selected per-recipient ringtone value.

Fixes #3397
Closes #3477

src/org/thoughtcrime/securesms/preferences/AdvancedRingtonePreference.java

@@ -0,0 +1,31 @@
+package org.thoughtcrime.securesms.preferences;
+
+import android.content.Context;
+import android.net.Uri;
+import android.preference.RingtonePreference;
+import android.util.AttributeSet;
+
+
+public class AdvancedRingtonePreference extends RingtonePreference {
+
+  private Uri currentRingtone;
+
+  public AdvancedRingtonePreference(Context context, AttributeSet attrs, int defStyleAttr) {
+    super(context, attrs, defStyleAttr);
+  }
+  public AdvancedRingtonePreference(Context context, AttributeSet attrs) {
+    super(context, attrs);
+  }
+  public AdvancedRingtonePreference(Context context) {
+    super(context);
+  }
+
+  @Override
+  protected Uri onRestoreRingtone() {
+    return currentRingtone;
+  }
+
+  public void setCurrentRingtone(Uri uri) {
+    currentRingtone = uri;
+  }
+}