Refactor Nearby Message listener

chrome/android/java/src/org/chromium/chrome/browser/physicalweb/PhysicalWebBleClient.java

Index: chrome/android/java/src/org/chromium/chrome/browser/physicalweb/PhysicalWebBleClient.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/physicalweb/PhysicalWebBleClient.java b/chrome/android/java/src/org/chromium/chrome/browser/physicalweb/PhysicalWebBleClient.java
index 2335cfcbfb25c12043ac47824352e99ddf5d7345..9ad9c8913e4dbb3d4746211d2cc98f362165f57e 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/physicalweb/PhysicalWebBleClient.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/physicalweb/PhysicalWebBleClient.java
@@ -34,6 +34,24 @@ public class PhysicalWebBleClient {
         public void onFound(Message message) {}
     }
 
+    protected static class BackgroundMessageListener extends MessageListener {
+        @Override
+        public void onFound(Message message) {
+            String url = PhysicalWebBleClient.getInstance().getUrlFromMessage(message);
+            if (url != null) {
+                UrlManager.getInstance().addUrl(new UrlInfo(url));
+            }
+        }
+
+        @Override
+        public void onLost(Message message) {
+            String url = PhysicalWebBleClient.getInstance().getUrlFromMessage(message);
+            if (url != null) {
+                UrlManager.getInstance().removeUrl(new UrlInfo(url));
+            }
+        }
+    };
+
     /**
      * Get a singleton instance of this class.
      * @return an instance of this class (or subclass).
@@ -89,6 +107,14 @@ public class PhysicalWebBleClient {
     }
 
     /**
+     * Create a MessageListener that listens during a background scan.
+     * @return the MessageListener.
+     */
+    MessageListener createBackgroundMessageListener() {
+        return new BackgroundMessageListener();
+    }
+
+    /**
      * Begin a foreground subscription to URLs broadcasted from BLE beacons.
      * This currently does nothing and should be overridden by a subclass.
      * @param activity The Activity that is performing the scan.