Fix NPE in MtpDocumentsProviderTests

Previous patch ag/2250238 broke MtpDocumentsProviderTests since
ServiceIntentSender's constructor refers the context argument which is
null in the tests.

The CL adds a test version of the constructor which does not use the
context argument in it.

Bug: 38363487
Test: MtpDocumentsProviderTests
Change-Id: I68a1d8cb6997499e5069c33f70fd0f675aaad77c
(cherry picked from commit c5949bd39c)

packages/MtpDocumentsProvider/src/com/android/mtp/ServiceIntentSender.java

@@ -23,6 +23,7 @@ import android.app.NotificationManager;
 import android.content.ComponentName;
 import android.content.Context;
 import android.content.Intent;
+import com.android.internal.annotations.VisibleForTesting;
 import com.android.internal.util.Preconditions;
 
 /**
@@ -30,7 +31,7 @@ import com.android.internal.util.Preconditions;
  */
 class ServiceIntentSender {
     private final static String CHANNEL_ID = "device_notification_channel";
-    private Context mContext;
+    private final Context mContext;
 
     ServiceIntentSender(Context context) {
         mContext = context;
@@ -46,6 +47,11 @@ class ServiceIntentSender {
         notificationManager.createNotificationChannel(mChannel);
     }
 
+    @VisibleForTesting
+    protected ServiceIntentSender() {
+        mContext = null;
+    }
+
     /**
      * Notify the change of opened device set.
      * @param records List of opened devices. Can be empty.

packages/MtpDocumentsProvider/tests/src/com/android/mtp/TestServiceIntentSender.java

@@ -17,10 +17,6 @@
 package com.android.mtp;
 
 class TestServiceIntentSender extends ServiceIntentSender {
-    TestServiceIntentSender() {
-        super(null);
-    }
-
     @Override
     void sendUpdateNotificationIntent(MtpDeviceRecord[] record) {}
 }